Croissant Egg Casserole with Mushrooms & Spinach

5 from 1 vote

This vegetarian breakfast egg casserole features sautéed spinach and mushrooms, buttery croissant pieces, and feta cheese.

Prep Time10

Cook Time30

Total Time40

Course: Breakfast

Cuisine: American

Diet: Vegetarian

Servings: servings

Calories: 509kcal

Preheat the oven to 350F. Cut or tear the croissants into 1-inch pieces. Set aside.
Heat a large skillet over medium heat. Drizzle with olive oil. Once hot, add the chopped mushrooms and diced onion. Cook until golden, about 6-8 minutes, then stir in the spinach, garlic, and ½ teaspoon of the salt. Continue cooking until the spinach is wilted and the garlic is golden. Remove from the heat.
While the mushrooms cook, whisk together the egg filling in a bowl until well combined: eggs, milk, remaining ½ teaspoon salt, optional red pepper flakes, and black pepper.
Grease a 9x9-inch or similarly sized baking dish, such as 8x11 or 10x10. Layer the cubed croissant pieces across the bottom of the dish. Top with the sautéed ingredients, then sprinkle with feta. Pour the egg mixture across the top of the veggies. The croissant pieces should be mostly covered, but its okay if some edges poke out.
Bake at 350F for 30 minutes, or until the eggs are completely set in the center and the edges are pulling away from the pan. If the croissants brown too quickly, loosely tent with a sheet of foil. Serve & enjoy!

How to freeze: Freeze the casserole in individual slices or as an an entire casserole. Cover with plastic wrap and foil, then freeze for up to 3 months. Let thaw in the fridge overnight before reheating.
To prep in advance: I don't recommend assembling the casserole ahead, as the croissants will soften too much. Instead, assemble everything except for the eggs in the casserole dish. Keep the egg mixture separate, pouring into the dish just before baking.
If the croissants are browned but the eggs aren't cooked through, tent the baking dish with foil.