Preheat your oven to 350°F (175°C).

Prepare your baking dish by lightly coating a 9x6 or 9x11 deep baking dish with cooking spray.

Layer the croissants by tearing them into halves and placing them in the prepared dish.

Chop the ham into thirds and distribute it evenly around the croissant layers.

Sprinkle shredded cheese generously over the croissants and ham.

Whisk together eggs, half and half, Dijon mustard, and salt in a separate bowl. Pour this creamy mixture evenly over the layered ingredients in the dish.

Cover the dish with foil and chill it in the refrigerator for 30 minutes to overnight.

Bake the casserole covered for 20 minutes, then remove the foil and continue baking for an additional 10-15 minutes until bubbly and golden brown.

Rest for 5 minutes before serving. Dust with powdered sugar for a sweet finish.