This French onion croissant bake is ideal for a special breakfast or brunch. It’s assembled ahead of time and baked just before serving. Savory, cheesy and utterly delicious!
Why is holiday brunch so wonderful?
This overnight French onion croissant bake is the ultimate holiday breakfast: prepared the night before, rich and indulgent, and perfect for feeding a crowd. It feels special and elegant while staying comforting and approachable.
I first made a similar overnight croissant breakfast casserole a few years ago and fell in love with it. We enjoy it so much I usually make it only on holidays — it’s rich, filling and universally loved. This year I turned it into a French onion version by swapping some of the greens for a generous amount of caramelized onions. The result tastes as good as it sounds.
How to make it
Start with the caramelized onions. This step takes time—about 60 to 90 minutes for three to four large sweet onions—but it’s worth it. Cook the onions over medium heat until soft, then lower the heat and continue slowly, stirring often, until they’re deeply golden and sweet. If they begin to stick or brown too quickly, lower the heat and add a splash of water.
One of the best parts is using croissants. Cut croissants in half and toast them under the broiler until they develop crisp, caramelized edges. Those toasted bits provide the perfect texture contrast.
The custard is a simple mixture of eggs, milk and heavy cream, with freshly grated gruyere folded in. The cheese melts into the custard and gives the bake a silky, souffle-like texture.
Combine the toasted croissant pieces, most of the caramelized onions, eggs and cheese in a buttered 9×13 baking dish. Press the croissant pieces so they soak up the custard, cover the dish and refrigerate overnight. Chilling is essential for the croissants to absorb the custard and for the flavors to meld.
In the morning, remove the dish from the fridge to take the chill off, top with the remaining cheese and remaining caramelized onions, and bake until golden and set. The top becomes beautifully golden and slightly crispy while the interior stays tender and custardy.
The finished bake is cheesy, melty, savory and slightly sweet from the onions. It’s a decadent, crowd-pleasing dish for holiday mornings or relaxed gatherings, and it feeds a lot of people.
This is a wonderful idea for a holiday brunch or for a cozy Christmas morning after a day of relaxation — satisfying, impressive and one of the best things to serve a crowd.
French Onion Croissant Bake
Overnight French Onion Croissant Bake
8 people
45 mins
45 mins
8 hrs
9 hrs 30 mins
Ingredients
- 3 tablespoons olive oil
- 4 large sweet onions, thinly sliced
- Kosher salt and pepper
- 5 to 7 large croissants, sliced in half lengthwise
- 2 garlic cloves, minced
- 8 large eggs
- 2 1/2 cups milk
- 1 cup heavy cream
- 8 ounces gruyere cheese, freshly grated
- 3 tablespoons chopped fresh thyme, plus more for topping
- Parmesan cheese for topping
Instructions
- Heat the olive oil in a large oven-safe skillet over medium heat. Add the sliced onions and a big pinch of salt. Cook, stirring often, until the onions soften, about 10–15 minutes.
- Reduce the heat to low or medium-low and continue to cook, stirring frequently, until the onions are deeply golden and caramelized, about 60–90 minutes. If they begin to burn, lower the heat or add a splash of water to loosen them.
- When the onions are caramelized, transfer them to a plate. (If you’re pressed for time, 1 teaspoon of sugar, honey or maple syrup can speed caramelization—stir often and monitor closely.)
- Preheat the oven to 450°F. Place croissant halves cut-side up on a baking sheet and toast for 5–8 minutes until golden and crisp. Let cool slightly, then tear or chop into pieces.
- Brush a 9×13 baking dish with melted butter. Toss the toasted croissant pieces with half the caramelized onions, making sure the onions are evenly distributed.
- In a large bowl, whisk together the eggs, milk, heavy cream, and a generous pinch of salt and pepper. Stir in 1 cup of grated gruyere and the chopped thyme. Reserve the remaining gruyere in the fridge for topping.
- Pour the egg mixture over the croissant mixture, pressing pieces into the liquid so they absorb it. Top with the remaining caramelized onions.
- Cover with plastic wrap and refrigerate for 8 hours or overnight.
- Preheat the oven to 350°F. Remove the casserole from the fridge 30 minutes before baking to take the chill off. Remove plastic wrap and top with the remaining grated gruyere.
- Bake uncovered for 45–60 minutes, until the center is set and the top is golden. Finish with a sprinkle of parmesan and fresh thyme before serving.
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Happy holidaying!