High-Protein Overnight Egg and Cheese Breakfast Casserole

Name: High-Protein Overnight Egg and Cheese Breakfast Casserole
Prep time: 20 min
Cook time: 50 min
Total time: 9 h 10 min
Yield: 8 servings
Cuisine: American
Ingredients: 8 slices whole grain sourdough bread (cut into 1-inch cubes, about 5 cups); 200 g turkey sausage (casings removed, crumbled and cooked); 2 cups fresh baby spinach (roughly chopped); 1 medium red bell pepper (finely diced); 3 spring onions (thinly sliced, plus extra to garnish); 2 cloves garlic (minced); 8 large whole eggs (free-range recommended); 1 cup low-fat cottage cheese (blended smooth); 1 cup semi-skimmed milk; 1 tsp Dijon mustard; 1 tsp smoked paprika; 0.5 tsp onion powder; 0.5 tsp garlic powder; 0.25 tsp black pepper; 0.5 tsp fine sea salt; 1.5 cups reduced-fat sharp cheddar cheese (freshly grated, divided); 1 tbsp olive oil (for cooking the sausage and vegetables)

High ProteinMeal PrepNut-Free

Prep Time20 min

Cook Time50 min

Servings8

Calories292 kcal

Health Score8/10

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High-Protein Overnight Egg and Cheese Breakfast Casserole

There is something genuinely magical about waking up knowing breakfast is already handled. This overnight egg and cheese breakfast casserole is one of those recipes that quietly does all the hard work while you sleep, so your morning feels calm and your kitchen stays clean. It is the kind of dish that makes you feel like you have your life together, even if you were scrambling to put it together at 10pm the night before.

Unlike traditional casseroles that lean heavily on white bread, full-fat sausage, and generous pours of cream, this version is built around smart swaps that genuinely boost nutrition without sacrificing comfort. We use hearty whole grain sourdough for extra fibre and a satisfying chew. The egg base is stretched with cottage cheese, which sounds surprising but melts invisibly into the custard while quietly doubling the protein content. Sharp reduced-fat cheddar and a little crumbled turkey sausage carry all the flavour you expect, and a generous pile of spinach, red pepper, and spring onions adds colour, vitamins, and texture. Every slice gives you a proper meal, not just a carb-heavy start that leaves you hungry by 10am.

The prep is genuinely simple. You layer everything into a baking dish the night before, pour the egg custard over the top, press it down gently, cover it, and refrigerate it overnight. The bread absorbs the egg mixture completely, which gives you that creamy, almost custardy interior that makes this casserole so satisfying. In the morning, you pull it out of the fridge, let it sit for about 15 minutes while your oven heats up, then bake until the top is golden and puffed. The smell alone will have everyone drifting to the kitchen. It feeds eight comfortably, which makes it ideal for family breakfasts, holiday mornings, brunch gatherings, or meal prepping a week of breakfasts for yourself.

Nutritionally, this casserole is a serious step up from most overnight breakfast bakes. Each serving lands around 290 calories with over 25 grams of protein, which is the kind of breakfast that actually keeps you full until lunch. The fibre from the whole grain bread and vegetables helps slow digestion, avoiding the blood sugar spike you get from refined carb-heavy versions. You can easily adapt it to suit your household. Swap the turkey sausage for extra vegetables if you prefer it fully vegetarian, or use a lactose-free cheese if dairy is a concern. Once you make this overnight egg and cheese breakfast casserole, it will earn a permanent spot in your weekly rotation.

Ingredients

Serves:8

8 slices whole grain sourdough bread (cut into 1-inch cubes, about 5 cups)
200 g turkey sausage (casings removed, crumbled and cooked)
2 cups fresh baby spinach (roughly chopped)
1 medium red bell pepper (finely diced)
3 spring onions (thinly sliced, plus extra to garnish)
2 cloves garlic (minced)
8 large whole eggs (free-range recommended)
1 cup low-fat cottage cheese (blended smooth)
1 cup semi-skimmed milk
1 tsp Dijon mustard
1 tsp smoked paprika
0.5 tsp onion powder
0.5 tsp garlic powder
0.3 tsp black pepper
0.5 tsp fine sea salt
1.5 cups reduced-fat sharp cheddar cheese (freshly grated, divided)
1 tbsp olive oil (for cooking the sausage and vegetables)

Instructions

1
Heat the olive oil in a non-stick frying pan over medium heat. Add the crumbled turkey sausage and cook for 5 to 6 minutes, breaking it up with a spoon, until browned and cooked through. Add the garlic, red pepper, and spring onions, cooking for another 2 minutes until softened. Stir in the spinach and cook for 1 minute until just wilted. Remove from the heat and set aside to cool slightly.
Letting the sausage and vegetable mixture cool before assembling prevents the egg custard from cooking prematurely when you pour it over.
2
Lightly grease a 9x13 inch baking dish with a little olive oil or a light spray of cooking oil. Spread the cubed whole grain sourdough bread in an even layer across the bottom of the dish.
Day-old bread works even better here if you have it, as it absorbs the custard more evenly without becoming too soggy.
3
Scatter the cooked sausage and vegetable mixture evenly over the bread cubes. Sprinkle one cup of the grated cheddar over the top of the sausage and vegetable layer, reserving the remaining half cup for the morning.
4
In a blender or using a stick blender, blend the cottage cheese until completely smooth. This takes about 30 seconds and ensures no lumps in your custard. In a large mixing bowl, whisk together the whole eggs, blended cottage cheese, semi-skimmed milk, Dijon mustard, smoked paprika, onion powder, garlic powder, salt, and black pepper until fully combined.
Blending the cottage cheese is the key step that makes this recipe work. Skipping it will leave small white curds in the custard, which affects the texture.
5
Pour the egg custard mixture evenly over the bread, sausage, and cheese layers in the baking dish. Use the back of a spoon or your clean hands to gently press the bread down into the liquid so every piece starts absorbing the custard. Cover the dish tightly with cling film or foil and refrigerate for at least 8 hours, or overnight.
If you are short on time, a minimum soak of 4 hours will still work, but overnight gives you the best texture.
6
When you are ready to bake, remove the casserole from the refrigerator and let it sit at room temperature for 15 minutes while you preheat your oven to 180 degrees Celsius (350 degrees Fahrenheit). Remove the covering from the dish.
Bringing the casserole to room temperature before baking helps it cook more evenly all the way through.
7
Sprinkle the reserved half cup of cheddar cheese evenly over the top of the casserole. Bake uncovered for 45 to 50 minutes, until the centre is set and no longer jiggly, and the top is golden brown and slightly puffed. A knife inserted into the centre should come out clean.
If the top is browning too fast before the centre is set, loosely tent the dish with foil for the last 10 minutes of baking.
8
Remove the casserole from the oven and allow it to rest for 10 minutes before slicing and serving. Scatter extra sliced spring onions over the top for freshness. Cut into 8 portions and serve warm.

Nutrition per serving

292kcal

Calories

26g

Protein

18g

Carbs

12g

Fat

Fibre

Sugar

520mg

Sodium

Pro Tips

✓
Freshly grating your cheddar from a block always melts more smoothly than pre-shredded cheese, which contains anti-caking agents that can make it grainy.
✓
Press the bread into the custard firmly before refrigerating. The more the bread absorbs overnight, the creamier the finished casserole will be.
✓
If you are making this for a large crowd, the recipe doubles well in two separate 9x13 dishes.
✓
Let the casserole rest for at least 10 minutes after baking. Cutting into it too soon will make it fall apart.
✓
Adding a pinch of chilli flakes to the egg mixture gives a gentle warmth that pairs beautifully with the smoked paprika.

Frequently Asked Questions

Can I make this overnight egg and cheese breakfast casserole without bread?↓

Yes, you can skip the bread entirely for a lower-carb version. Simply increase the eggs by two and add an extra cup of vegetables to compensate for the volume. The texture will be closer to a frittata than a traditional casserole, but it is still delicious.

Can I use egg whites only to reduce calories further?↓

You can replace up to half the whole eggs with egg whites. A good ratio is 4 whole eggs plus 6 egg whites. Using all egg whites will reduce the fat content but also makes the texture slightly rubbery, so a mix is best.

How do I know when the casserole is fully cooked?↓

The casserole is ready when the centre no longer jiggles when you gently shake the dish, the top is golden, and a knife inserted into the middle comes out clean. If in doubt, an internal temperature of 74 degrees Celsius (165 degrees Fahrenheit) confirms it is fully set.

Can I freeze this breakfast casserole?↓

Yes, this casserole freezes very well. Bake it first, let it cool completely, then slice into individual portions and wrap each one tightly. Freeze for up to 2 months. Reheat individual portions in a 170 degree Celsius oven for 15 to 20 minutes, or microwave for 2 to 3 minutes.

What cheese works best in this recipe?↓

Reduced-fat sharp cheddar is the top choice here because its bold flavour means you need less of it to get a satisfying cheesy result. Gruyere, smoked gouda, or pepper jack also work beautifully if you want to mix things up.

Can I assemble this the morning of instead of overnight?↓

You can, but allow at least 30 minutes of soaking time before baking if you are in a rush. The longer the bread soaks, the creamier and more custardy the result. Overnight is genuinely worth it if you can plan ahead.

Variations

•
Fully Vegetarian
Omit the turkey sausage and replace it with one cup of diced courgette and a handful of sun-dried tomatoes. Add an extra half teaspoon of smoked paprika to keep the depth of flavour.
•
Spicy Southwest
Add a small tin of diced green chillies and half a teaspoon of cumin to the egg mixture. Swap the cheddar for a pepper jack blend and top the finished casserole with a spoonful of plain Greek yogurt and fresh coriander.
•
Greek-Inspired
Replace the cheddar with crumbled feta cheese and add a cup of halved cherry tomatoes, diced cucumber, and a handful of kalamata olives. Use dried oregano in place of smoked paprika for a Mediterranean flavour profile.
•
Gluten-Free
Substitute the whole grain sourdough with your favourite certified gluten-free bread. The rest of the recipe remains exactly the same, and the texture is nearly identical once baked.

Substitutions

•
Turkey sausage → Chicken sausage or extra vegetables (Chicken sausage works as a direct swap. For a vegetarian version, use diced mushrooms and courgette instead, cooked until the moisture has evaporated.)
•
Low-fat cottage cheese → Plain low-fat Greek yogurt (Greek yogurt adds a slight tang and similar protein boost. Blend it with the eggs just as you would the cottage cheese.)
•
Semi-skimmed milk → Unsweetened oat milk or almond milk (Unsweetened oat milk works very well here and keeps the casserole dairy-light. Avoid sweetened plant milks as they will affect the flavour.)
•
Whole grain sourdough → Gluten-free bread or whole wheat toast (Any sturdy bread will work. Avoid very soft sandwich bread as it can become too soggy after the overnight soak.)
•
Reduced-fat cheddar → Full-fat cheddar or Gruyere (Full-fat cheddar adds a little more richness if you prefer. Gruyere gives a nuttier, more complex flavour that works beautifully with the smoked paprika.)

🧊 Storage

Store leftover casserole in an airtight container in the refrigerator for up to 4 days. Reheat individual slices in the microwave for 90 seconds to 2 minutes, or in a 170 degree Celsius oven for 12 to 15 minutes until heated through. The casserole also freezes well for up to 2 months when wrapped in individual portions.

📅 Make Ahead

This recipe is specifically designed to be made ahead. Assemble the casserole the evening before, cover tightly, and refrigerate for 8 to 12 hours. In the morning, remove from the fridge, let it rest at room temperature for 15 minutes, top with the reserved cheese, and bake as directed. You can also fully bake the casserole up to 2 days in advance and reheat it gently before serving.