Step 1: Grease a 9x13-inch baking dish with 1 tablespoon of melted butter or non-stick spray.
Step 2: Arrange the bread cubes evenly in the prepared baking dish.
Step 3: In a large bowl, whisk together the eggs, whole milk, heavy cream, granulated sugar, brown sugar, vanilla extract, cinnamon, and salt until well combined and smooth.
Step 4: Pour the egg mixture evenly over the bread cubes, making sure all the bread is well saturated. Gently press down on the bread with a spatula to ensure it absorbs the liquid.
Step 5: Cover the baking dish tightly with plastic wrap and refrigerate for at least 4 hours, or preferably overnight (up to 12 hours). This soaking time is crucial for a custardy french toast recipe casserole.
Step 6: The next morning, preheat your oven to 375°F (190°C).
Step 7: Remove the casserole from the refrigerator and uncover. Drizzle the remaining 1 tablespoon of melted butter over the top of the bread.
Step 8: Bake, uncovered, for 45-55 minutes, or until the french toast recipe casserole is golden brown, puffed, and a knife inserted into the center comes out clean (no liquid egg mixture). If the top browns too quickly, you can loosely tent it with aluminum foil.
Step 9: Let the french toast recipe casserole rest for 5-10 minutes before serving. This allows the custard to set. Serve warm with your favorite toppings like powdered sugar, maple syrup, fresh berries, or whipped cream.