Make Ahead Christmas Breakfast Casserole with Eggs and Vegetables
Christmas morning should feel magical, not stressful. The last thing you want to be doing while the kids are tearing into their presents is chopping onions and whisking eggs from scratch. That is exactly why this make ahead Christmas breakfast casserole with eggs and vegetables was designed to do all the hard work the night before, so you can wake up, slide it into the oven, and actually enjoy the morning. It smells incredible as it bakes, filling the kitchen with the kind of warmth that makes the whole day feel special.
What makes this casserole genuinely healthier than the classic versions you might have grown up with is the combination of choices made at every step. Instead of a heavy bread base soaked in cream, this recipe uses a thin layer of diced sweet potato as the foundation. Sweet potato brings natural sweetness, a good dose of fibre, and a lower glycaemic load than white bread. The egg mixture is built on whole eggs plus extra egg whites, which boosts the protein content significantly without piling on extra saturated fat. A splash of unsweetened almond milk keeps the custard light and silky. The cheese is sharp reduced-fat cheddar, used sparingly so every bite still tastes indulgent but without the calorie overload of a full-fat heavy layer.
The vegetables are where this casserole really shines at Christmas. Red and green bell peppers bring natural colour that looks genuinely festive in the dish, almost like a wreath when you scatter them across the top. Baby spinach wilts down into the egg mixture and disappears slightly, adding iron and folate without anyone noticing. Mushrooms contribute a satisfying savoury depth and help the casserole feel hearty even though it is not loaded with processed meat. Turkey sausage crumbled through the middle layer adds that comforting, crowd-pleasing sausage flavour with a much leaner protein profile than traditional pork sausage. A little smoked paprika and dried thyme in the seasoning give the whole dish a warmth that feels right for the season.
Assembling everything the night before takes about fifteen minutes. You layer it up, cover the dish tightly, and refrigerate it overnight. The next morning it goes straight from the fridge into a preheated oven. It does need a slightly longer bake time when going in cold, which is accounted for in the instructions below. The result is a golden, puffed casserole with a set custard centre, crispy edges, and a surface that turns a beautiful deep golden brown. It slices cleanly into twelve generous portions, making it ideal for feeding a crowd at the table. Leftovers reheat brilliantly throughout the following days, so nothing goes to waste after the festivities.
Ingredients
- 2 medium sweet potatoes (peeled and diced into small 1cm cubes)
- 1 tbsp olive oil (for roasting the sweet potato)
- 400 g lean turkey sausage (casings removed if applicable, crumbled)
- 1 tsp olive oil (for cooking the turkey sausage)
- 1 large red bell pepper (diced)
- 1 large green bell pepper (diced)
- 1 medium yellow onion (finely diced)
- 200 g chestnut mushrooms (sliced)
- 100 g baby spinach (roughly chopped)
- 3 cloves garlic (minced)
- 8 large whole eggs (free range if possible)
- 6 large egg whites (from fresh eggs or carton)
- 180 ml unsweetened almond milk (or any unsweetened plant milk)
- 1 tsp smoked paprika
- 1 tsp dried thyme
- 0.5 tsp garlic powder
- 0.5 tsp fine sea salt (adjust to taste)
- 0.3 tsp black pepper (freshly ground)
- 100 g reduced fat sharp cheddar (grated, divided)
- 2 tbsp fresh chives (chopped, for serving)
- 1 spray cooking spray (for greasing the baking dish)
Instructions
- 1
Preheat your oven to 200C (180C fan, 400F). Toss the diced sweet potato with 1 tablespoon of olive oil and a pinch of salt and pepper on a baking tray. Spread into a single layer and roast for 20 minutes until just tender and lightly golden at the edges. Remove and set aside to cool slightly.
Do not overcook the sweet potato at this stage as it will continue cooking inside the casserole.
- 2
While the sweet potato roasts, heat 1 teaspoon of olive oil in a large non-stick skillet over medium-high heat. Add the crumbled turkey sausage and cook, breaking it up with a wooden spoon, for 6 to 8 minutes until fully cooked through and lightly browned. Transfer to a plate lined with kitchen paper and set aside.
Turkey sausage can stick more than pork sausage, so keep the heat at medium-high and stir regularly.
- 3
In the same skillet, add the diced onion and cook for 3 minutes until softened. Add the garlic, red and green bell peppers and mushrooms. Cook for another 5 minutes, stirring occasionally, until the vegetables are tender and any moisture from the mushrooms has evaporated. Stir in the baby spinach and cook for 1 minute until wilted. Remove from heat.
Letting the mushroom moisture cook off is important so the casserole does not turn watery.
- 4
Spray a 9x13 inch (23x33cm) baking dish generously with cooking spray. Spread the roasted sweet potato cubes evenly across the bottom of the dish as your base layer.
- 5
Scatter the cooked turkey sausage evenly over the sweet potato. Then spoon the sauteed vegetable mixture over the top, spreading it out evenly. Sprinkle half of the grated cheddar over the vegetables.
- 6
In a large bowl, whisk together the whole eggs, egg whites, almond milk, smoked paprika, dried thyme, garlic powder, salt and black pepper until well combined and slightly frothy. Pour this egg mixture evenly over the layered ingredients in the baking dish.
Pour slowly and allow the egg mixture to settle down through all the layers rather than pooling on top.
- 7
Scatter the remaining cheddar across the top of the casserole. Cover the dish tightly with cling film or a fitted lid and refrigerate overnight, or for at least 8 hours.
Press the cling film directly onto the surface if you want to avoid any skin forming on the egg mixture, though this is mostly cosmetic.
- 8
On Christmas morning, remove the casserole from the fridge while the oven preheats to 180C (160C fan, 350F). Remove the cling film. Bake uncovered for 50 to 55 minutes until the top is deep golden brown, the edges are set and a knife inserted into the centre comes out clean with no liquid egg.
If the top is browning too quickly before the centre sets, loosely tent a piece of foil over the dish for the last 15 minutes.
- 9
Allow the casserole to rest for 5 to 10 minutes before slicing. Scatter fresh chives over the top and cut into 12 squares. Serve warm directly from the dish.
Resting allows the custard to firm up fully so slices hold together cleanly when lifted.
Nutrition per serving
218kcal
Calories
22g
Protein
14g
Carbs
8g
Fat
3g
Fibre
5g
Sugar
390mg
Sodium
Pro Tips
- ✓
Roast the sweet potato until just tender at step one. Overcooking it turns it mushy inside the casserole.
- ✓
The overnight chill is key. The egg mixture soaks into all the layers and the whole casserole becomes more cohesive and flavourful.
- ✓
Use a sharp reduced-fat cheddar rather than a mild one. You get far more flavour from a smaller quantity, which keeps calories down.
- ✓
If you are feeding a crowd, this casserole doubles well. Use two dishes and stagger the baking if your oven is not large enough for both at once.
- ✓
Let the baked casserole rest for at least 5 minutes before slicing. This prevents the squares from falling apart when served.
- ✓
Add a pinch of dried chilli flakes to the egg mixture if you like a subtle festive warmth in the background.
- ✓
Grate your own cheese rather than using pre-grated. Pre-grated cheese contains anti-caking agents that can affect how it melts.
Frequently Asked Questions
Variations
- •
Dairy Free Version
Swap the reduced-fat cheddar for a good quality dairy-free cheddar-style cheese. Use oat milk or unsweetened coconut milk instead of almond milk. All other components are already dairy free.
- •
Extra Greens Version
Double the spinach and add a large handful of finely chopped kale alongside it. Massage the kale briefly before adding to soften it. This version is even higher in fibre and antioxidants.
- •
Spicy Festive Version
Add half a teaspoon of dried chilli flakes and a diced jalapeño to the vegetable sauté. Swap the cheddar topping for a light scatter of crumbled feta. The salty tang of feta with the heat creates a brilliant flavour contrast.
- •
Fully Vegetarian Version
Simply leave out the turkey sausage entirely and add an extra 150g of mushrooms plus a drained and rinsed tin of black beans for protein. The casserole stays hearty, high protein and completely meat free.
Substitutions
- •Sweet potato base → Baby potatoes, halved and par-boiled (Slightly higher in glycaemic index but still a wholesome option. Par-boil for 8 minutes before using.)
- •Turkey sausage → Chicken sausage or chicken mince seasoned with fennel and sage (Both work brilliantly. Season the chicken mince with half a teaspoon of fennel seeds and a pinch of sage to mimic sausage flavour.)
- •Reduced fat cheddar → Gruyere or light mozzarella (Gruyere melts beautifully and adds a nuttier flavour. Mozzarella makes a milder, stretchier top layer.)
- •Unsweetened almond milk → Skimmed cow's milk or unsweetened oat milk (All give a similarly light custard. Avoid full fat cream as it significantly increases the calorie count.)
- •Baby spinach → Kale or Swiss chard (Both work well but need a slightly longer sauté time to soften fully, about 3 minutes compared to 1 minute for spinach.)
- •Chestnut mushrooms → Portobello mushrooms or shiitake mushrooms (Portobello gives a meatier texture. Shiitake adds a deeper umami flavour that works well in the savoury egg mixture.)
🧊 Storage
Store leftover casserole covered in the refrigerator for up to 4 days. Reheat individual portions in the microwave for 90 seconds to 2 minutes or in the oven at 160C for 15 minutes. For longer storage, freeze individual slices wrapped tightly for up to 2 months. Always reheat until piping hot throughout before serving.
📅 Make Ahead
Assemble the entire casserole the night before Christmas, cover tightly with cling film and refrigerate for 8 to 24 hours. On Christmas morning, remove from the fridge while the oven preheats. Bake straight from cold at 180C for 50 to 55 minutes. Alternatively, bake it fully the day before, refrigerate and simply reheat on Christmas morning at 160C covered in foil for 20 to 25 minutes.
