Making Overnight Croissant Breakfast Casserole is straightforward. Follow these steps to ensure your dish turns out perfectly:

1. Prepare the Baking Dish: Grease a 9×13-inch baking dish with butter or cooking spray.
2. Cut the Croissants: Tear or cut the croissants into small, bite-sized pieces. Spread them evenly across the baking dish.
3. Mix Eggs and Milk: In a large bowl, whisk together the eggs, milk, Dijon mustard, garlic powder, onion powder, salt, and pepper until well combined.
4. Add the Fillings: Stir in the cooked sausage (or ham), chopped spinach (or other vegetables), and half of the shredded cheese into the egg mixture.
5. Combine: Pour the egg mixture evenly over the croissant pieces. Press the croissants down gently to ensure they soak up the egg mixture.
6. Top with Cheese: Sprinkle the remaining cheese over the top of the casserole.
7. Cover and Chill: Cover the dish with plastic wrap or aluminum foil and refrigerate overnight (at least 8 hours).
8. Preheat the Oven: On the morning you wish to serve, preheat your oven to 350°F (175°C).
9. Uncover and Bake: Remove the cover from the casserole, and bake for 35-40 minutes or until the center is set and the top is golden brown.
10. Garnish: Once out of the oven, allow it to cool for a few minutes, then sprinkle with fresh herbs before serving.

By following these steps, you’ll have created an incredible breakfast casserole that is sure to delight!