Mushroom and Gruyère Croissant Breakfast Casserole

Heat the olive oil in a large skillet over medium heat. Add the sliced mushrooms and chopped onion.
Sauté until the mushrooms are tender and the onions are soft, about 5-7 minutes. Season with a pinch of salt and pepper. Remove from heat and set aside.
Step 2: Prepare the Casserole
In a large bowl, whisk together the eggs, milk, Dijon mustard, salt, and pepper.
In a greased 9×13-inch baking dish, spread the croissant chunks evenly across the bottom.
Add the sautéed mushrooms and onions over the croissants, then sprinkle with shredded Gruyère cheese.
Step 3: Assemble the Casserole
Pour the egg mixture over the croissants and vegetables, making sure to coat everything evenly.
Press down lightly on the croissants to help them absorb the egg mixture.
Cover with plastic wrap or foil and refrigerate for at least 2 hours (or overnight for best results).
Step 4: Bake the Casserole
Preheat your oven to 350°F (175°C).
Remove the casserole from the fridge and bake for 35-40 minutes, or until the eggs are fully set and the top is golden and bubbly.
Let it cool for a few minutes before slicing.
Step 5: Serve
Garnish with fresh parsley before serving.
Serving and Storage Tips