Preheat the oven to 350°F (175°C) and grease the baking dish with butter or non-stick spray.
Tear the croissants into bite-sized pieces and evenly distribute them in the prepared baking dish.
In a large mixing bowl, whisk together the eggs, whole milk, heavy cream, granulated sugar, vanilla extract, ground cinnamon, and salt until well combined.
Pour the custard mixture over the torn croissants, ensuring all pieces are soaked. Gently press down on the croissants to help them absorb the mixture.
Cover the dish with aluminum foil and let it sit for about 15 minutes to soak into the croissants, or refrigerate for up to overnight for deeper flavor.
Remove the foil and bake in the preheated oven for 30-35 minutes, or until the top is golden brown and a toothpick inserted in the center comes out clean.
Allow the casserole to cool for a few minutes before serving.
Serve warm with maple syrup drizzled on top, and optionally sprinkle powdered sugar and fresh berries.