Let's cook.
Preheat your oven to 375°F (190°C). Lightly grease an 8x8 inch baking dish.
Tear the croissants into large, bite-sized pieces and scatter half of them evenly in the prepared baking dish.
Layer the sliced ham over the croissant pieces, then sprinkle half of the shredded Gruyere cheese on top of the ham.
Add the remaining croissant pieces over the cheese layer, then top with the rest of the Gruyere cheese.
In a medium bowl, whisk together the eggs, milk, Dijon mustard, salt, and black pepper until well combined.
Pour the egg mixture evenly over the croissant, ham, and cheese layers in the baking dish, ensuring all pieces are moistened.
Bake for 25 minutes, or until the top is golden brown and the egg mixture is set and bubbly.
Save this recipe so you can find it again.