Prepare the Croissants. Tear the croissants into halves and place them in a greased 9x13-inch baking dish.
Make the Custard. In a large mixing bowl, whisk together eggs, milk, heavy cream, sugar, vanilla extract, cinnamon, and salt until well combined.
Assemble the Casserole. Pour the custard mixture evenly over the croissants, ensuring each piece is well soaked. Let the mixture sit for at least 20 minutes, or cover and refrigerate overnight for enhanced flavor.
Bake to Perfection. Preheat the oven to 350°F. Drizzle melted butter over the casserole and bake for 35-40 minutes until golden brown and set in the center.
Serve and Enjoy. Allow the casserole to cool slightly before dusting with powdered sugar and adding your favorite toppings. Serve warm with maple syrup.