Veggie Croissant Breakfast Casserole Recipe

Flaky croissants, fresh veggies, and baked eggs make this easy breakfast casserole feel rich but light. Perfect for a weekend brunch, or a luxurious weekday breakfast!

I'm a sucker for savory breakfasts, as evident in my Texas French toast casserole and bacon French toast casserole, but this recipe has become my favorite morning meal when I feel guilty about eating too much meat the day before and need to balance it out with vegetables. It's my way of convincing myself I'm being healthy while still having something buttery and flavorful.

The whole idea came about after a barbecue weekend when I woke up Monday morning craving something savory but also wanting to redeem myself from the day before. I had leftover croissants and a bunch of cherry tomatoes that needed using up. Throwing them together in a cast iron skillet with some eggs and cheese seemed like the perfect idea.

The tomatoes get all sweet and jammy in the oven, and the sautéed onions add this caramelized flavor that makes all the difference. My daughter now calls it "fancy breakfast" and I'm actually surprised that she is the one requesting it, she loves having it with a slice of sausage.

This casserole has everything I want in a morning meal: it feels hearty, it has real vegetables, and it's all wrapped in melted cheddar and buttery croissant. My husband likes to joke that it’s my idea of eating a salad... which, honestly, isn’t totally wrong.

Ingredients

The croissants are the foundation of this casserole. Their buttery layers soak up the egg mixture while staying tender, giving the dish a light texture instead of making it heavy like bread sometimes can. If croissants aren’t available, brioche or challah can work as a substitute, but they bring a slightly denser feel.

The sharp cheddar cheese adds a strong, savory flavor that ties everything together. Mild cheddar melts the same way, but it won’t have the same depth. You could even use a mix of cheddar and Gruyère if you want a hint of nuttiness.

Then, cherry tomatoes are what keep the dish bright. They soften in the oven and release just enough juice to balance the richness. Regular diced tomatoes can be used, but they tend to release more liquid and can make the casserole softer and more watery than intended.

See the recipe card for exact quantities.

Step-by-step Instructions

Here’s how to bring together a veggie croissant breakfast casserole that feels fresh but still easy enough for a weekend morning. 

Preheat the Oven and Prepare the Skillet

Set your oven to 375°F (190°C) so it’s fully heated by the time you’re ready to bake. Lightly grease a 10-inch cast iron skillet with oil or butter, making sure to coat the bottom and sides so nothing sticks during cooking.

Cook the Vegetables

Add the diced onions to the skillet and sauté over medium heat for about 10 minutes, stirring often, until they turn golden and soft. Add the cherry tomatoes and continue cooking for another 3 minutes. Season the mixture lightly with salt and pepper, then remove the vegetables from the skillet and set them aside for later.

Layer the Croissants and Eggs

Place the halved croissants in the bottom of the skillet, arranging them so the surface is covered evenly. Crack the eggs directly over the croissants, spacing them out so each serving will have its own egg.

Add Toppings

Sprinkle the cooked onions and tomatoes back into the skillet, then scatter the remaining cherry tomatoes, any extra vegetables you’re using like mushrooms, and the shredded cheddar cheese over and around the eggs. Lay a few thyme sprigs on top for flavor as the casserole bakes.

Bake the Casserole

Place the skillet on a baking sheet to catch any drips, then transfer it to the center rack of the oven. Bake for 12–18 minutes, depending on how set you like your eggs.

Finish and Serve

Carefully remove the skillet from the oven. Season the top with a pinch of sea salt and freshly ground black pepper. Add slices of avocado and any fresh herbs you like before serving straight from the skillet while it’s still hot.

Storage

This veggie croissant breakfast casserole is best enjoyed right after baking, while the croissants are still crisp around the edges. If you have leftovers, let them cool to room temperature before storing. Transfer the pieces to an airtight container and refrigerate for up to 2 days.

When reheating, place a portion in the oven at 350°F (175°C) for about 10 minutes to bring back some of the croissant’s texture. The microwave will warm it faster, but the croissants may turn a bit softer. Freezing isn’t recommended because the croissants lose their flaky layers and the eggs can become watery once thawed.

Recipe