Creating the Gruyère and Prosciutto Croissant Bake is easy if you follow these straightforward steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C).
2. Prepare the Dish: Grease a 9×13 inch baking dish with butter or cooking spray.
3. Cut the Croissants: Slice the croissants in half lengthwise and place them in the prepared baking dish, cut side up.
4. Layer Ingredients: Begin layering the prosciutto slices on top of the croissant halves, followed by an even sprinkle of grated Gruyère cheese.
5. Whisk Eggs: In a large bowl, whisk together the eggs, whole milk, Dijon mustard, salt, black pepper, and dried thyme until well combined.
6. Pour Custard Mixture: Carefully pour the egg mixture over the croissants, making sure to cover all the croissant halves.
7. Press Down: Gently press down on the croissants to help them soak up the egg mixture. Let it sit for 15 minutes.
8. Bake: Place the baking dish in the preheated oven and bake for 30-35 minutes or until the top is golden brown and set.
9. Cool Slightly: Remove from the oven and allow it to cool for 5-10 minutes before slicing.
10. Garnish and Serve: Optionally, sprinkle fresh parsley on top. Serve warm and enjoy!