Caramelized Onion Mushroom and Gruyere Breakfast Quiche with Oat Crust
There is something almost magical about the smell of onions slowly turning golden in a pan. Add earthy mushrooms and nutty gruyere to that picture, and you have the kind of breakfast that makes people stop whatever they are doing and come to the table. This caramelized onion mushroom and gruyere breakfast quiche delivers all of that warmth and richness while keeping the nutrition profile genuinely impressive. We are talking higher protein, more fibre, and significantly fewer calories than a classic quiche, all without sacrificing the deeply savoury flavour that makes this dish so satisfying.
The crust here is the first big upgrade. Instead of a butter-heavy shortcrust pastry, we use a combination of rolled oats and whole wheat flour blended with just a small amount of cold butter and low-fat Greek yogurt. This swap brings in extra fibre and protein while creating a pleasantly nutty, slightly crisp base that holds the filling beautifully. The oat crust does not puff or shrink dramatically the way some pastry crusts can, which means every slice holds its shape well, something you will definitely appreciate if you are meal-prepping for the week ahead.
The filling is where the real flavour building happens. Onions are cooked low and slow in olive oil until they turn a deep amber colour, developing natural sweetness without any added sugar. A generous handful of mixed mushrooms goes in next, cremini for earthiness, shiitake for a meaty chew, adding bulk and a satisfying umami depth that makes this quiche feel hearty. The egg base swaps heavy cream for a blend of whole eggs, egg whites, and unsweetened almond milk, keeping the texture custardy and rich while cutting saturated fat considerably. A small but punchy amount of grated gruyere cheese is stirred directly into the filling and scattered on top, so every bite carries that signature nutty, slightly sweet cheese flavour. Fresh thyme and a pinch of smoked paprika round everything out with a gentle herbal warmth.
This quiche works brilliantly for meal prep. Bake it on a Sunday and you have breakfast sorted for several days running. It reheats well in a low oven or even a microwave at reduced power, and the flavour actually deepens overnight as the filling settles. Serve it with a simple green salad or some sliced tomatoes for a complete, balanced morning meal. Each slice delivers around 22 grams of protein, which will keep you energised and full well past the mid-morning slump. Whether you are feeding a crowd at brunch or simply treating yourself to a proper sit-down breakfast on a weekday, this quiche is the kind of recipe that earns a permanent spot in your rotation.
Ingredients
- 3 cup rolled oats (old-fashioned, not instant)
- 1 cup whole wheat flour
- 1 tsp fine sea salt (for crust)
- 2 tbsp cold unsalted butter (cut into small cubes)
- 3 tbsp low-fat plain Greek yogurt (cold, used in place of buttermilk)
- 1 tbsp ice cold water (add only if dough feels dry)
- 1 tbsp olive oil (divided)
- 2 large yellow onions (thinly sliced into half moons)
- 8 oz mixed mushrooms (cremini and shiitake, roughly sliced)
- 2 cloves garlic (minced)
- 1 tbsp fresh thyme leaves (or 1 tsp dried thyme)
- 1 tsp smoked paprika
- 1 tsp fine sea salt (for filling)
- 1 tsp black pepper (freshly ground)
- 4 large whole eggs
- 3 large egg whites (boosts protein, reduces fat)
- 1 cup unsweetened almond milk (or any low-fat plant milk)
- 1 cup low-fat plain Greek yogurt (stirred into egg base for creaminess)
- 2 cup gruyere cheese (freshly grated, divided)
Instructions
- 1
Preheat your oven to 400 degrees F (200 degrees C) and lightly spray a 9-inch pie dish with cooking spray.
A glass or ceramic pie dish works best here as it distributes heat evenly for a crisper oat crust base.
- 2
Make the oat crust. Add the rolled oats, whole wheat flour and salt to a food processor and pulse 4 times to combine. Add the cold butter cubes and pulse about 10 to 12 times until the mixture looks like coarse, pebbly crumbs. Add the cold Greek yogurt and pulse 3 to 4 more times until the dough just begins to come together. If it seems dry, add the ice cold water one teaspoon at a time.
Do not over-process. Some larger crumbly bits are totally fine and will give the crust a lovely rustic texture.
- 3
Turn the dough out onto a piece of parchment paper, press it into a rough ball, and place a second sheet of parchment on top. Roll it out into a circle about 10 to 11 inches in diameter. Peel off the top layer of parchment, then carefully flip the crust into the prepared pie dish. Press it gently into the base and up the sides, patching any cracks with your fingers.
Chilling the formed crust in the fridge for 10 minutes before blind baking helps it hold its shape.
- 4
Blind bake the crust. Prick the base all over with a fork, then bake for 10 minutes. Remove from the oven and allow to cool slightly while you prepare the filling. Reduce oven temperature to 375 degrees F (190 degrees C).
- 5
Caramelize the onions. Heat 2 teaspoons of the olive oil in a large non-stick skillet over medium-low heat. Add the sliced onions and a small pinch of salt. Cook, stirring every 4 to 5 minutes, for 30 to 35 minutes until the onions are deep golden amber and very soft. Low and slow is the key here.
Resist the urge to rush this step on high heat. True caramelization takes time and that is where all the sweetness and depth comes from.
- 6
Once the onions are caramelized, push them to one side of the pan and add the remaining teaspoon of olive oil. Add the mushrooms and cook over medium heat for 5 to 6 minutes, stirring occasionally, until they have released their liquid and are golden at the edges. Add the garlic and cook for 1 minute more. Stir in the thyme, smoked paprika, salt and black pepper. Remove from heat.
Letting the mushrooms sit undisturbed for a minute or two before stirring encourages better browning.
- 7
Make the egg base. In a medium bowl, whisk together the whole eggs, egg whites, almond milk and Greek yogurt until smooth and combined. Season with a small pinch of salt and pepper. Stir in half the grated gruyere.
Whisking the yogurt into the egg mixture rather than the filling keeps the custard texture smooth and consistent.
- 8
Assemble the quiche. Spread the caramelized onion and mushroom mixture evenly across the pre-baked crust. Pour the egg mixture gently over the top, allowing it to settle between the vegetables. Scatter the remaining gruyere cheese evenly across the surface.
- 9
Bake at 375 degrees F for 30 to 35 minutes, until the centre is just set with a very slight wobble and the top is golden. A knife inserted in the centre should come out clean.
Check at the 28-minute mark. Overbaking will dry out the custard, so err on the side of pulling it slightly early.
- 10
Let the quiche rest on a wire rack for at least 10 minutes before slicing. This allows the custard to fully set and makes for cleaner, neater slices.
The quiche will continue to firm up as it cools, so do not worry if it looks slightly soft when it first comes out.
Nutrition per serving
285kcal
Calories
22g
Protein
18g
Carbs
13g
Fat
3g
Fibre
4g
Sugar
390mg
Sodium
Pro Tips
- ✓
Grate your gruyere fresh from a block rather than using pre-shredded cheese. Pre-shredded varieties contain anti-caking agents that can affect how the cheese melts.
- ✓
Do not skip resting the quiche after baking. Ten minutes makes a real difference to both texture and how cleanly it slices.
- ✓
For maximum caramelized onion flavour, use two onions rather than one. They cook down significantly and the result is absolutely worth the extra prep.
- ✓
The oat crust can be made the night before and stored in the fridge, wrapped tightly, ready to roll out and bake the next morning.
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If your filling looks very full before baking, place the pie dish on a baking sheet to catch any drips in the oven.
Frequently Asked Questions
Variations
- •
Spinach and Gruyere Addition
Stir 2 large handfuls of fresh baby spinach into the mushroom mixture during the last minute of cooking. It wilts quickly and adds extra iron, folate and colour to each slice.
- •
Sun-Dried Tomato and Herb
Add 3 tablespoons of chopped oil-packed sun-dried tomatoes to the filling along with a tablespoon of fresh basil. This gives the quiche a Mediterranean twist with bright acidity that complements the gruyere beautifully.
- •
Crustless High-Protein Version
Skip the oat crust entirely and pour the filling directly into a well-greased pie dish. This makes the quiche naturally gluten-free, saves roughly 80 calories per slice, and is even simpler to prepare.
- •
Turkey Sausage and Mushroom
Brown 150 grams of crumbled turkey sausage in the pan before adding the onions. Drain off any excess fat, then continue with the recipe as written. This bumps the protein content up further and makes each slice even more substantial.
Substitutions
- •Gruyere cheese → Swiss cheese or comte (Both melt well and carry a similar nutty sweetness. Aged white cheddar works too for a sharper finish.)
- •Unsweetened almond milk → Low-fat dairy milk or oat milk (Any unsweetened, unflavoured milk works here. Avoid sweetened varieties as they will affect the savoury balance.)
- •Whole wheat flour → Certified gluten-free oat flour (Use the same quantity for a gluten-free crust. The texture will be slightly more crumbly but still holds together well.)
- •Fresh thyme → Fresh rosemary or dried thyme (Use fresh rosemary sparingly as it is more intense. If using dried thyme, one teaspoon is equivalent to one tablespoon fresh.)
- •Low-fat Greek yogurt → Low-fat sour cream or kefir (Both provide a similar tang and creamy texture in both the crust and egg base. Full-fat versions work too but will increase the calorie count.)
🧊 Storage
Store cooled quiche covered in the refrigerator for up to 4 days. Reheat slices in a 325 degree F oven for 10 to 12 minutes or in the microwave at reduced power. For freezing, wrap tightly in cling film and foil and freeze for up to 2 months. Thaw overnight in the fridge before reheating.
📅 Make Ahead
The caramelized onions and sauteed mushrooms can be cooked up to 2 days ahead and stored in an airtight container in the fridge. The oat crust dough can be made the night before, wrapped and refrigerated. The fully baked quiche keeps well for 4 days, making it an excellent meal prep breakfast option.
