Arrange the bread slices in a single layer in the prepared baking dish.
In a large bowl, whisk together the eggs, milk, granulated sugar, cinnamon, nutmeg, and vanilla extract until well combined.
Pour the egg mixture evenly over the bread slices, ensuring all pieces are coated. Press down gently to help the bread absorb the liquid.
Drizzle the melted butter over the top of the casserole.
Cover the dish and refrigerate for at least 30 minutes, or preferably overnight, to allow the bread to soak up the custard.
Preheat your oven to 350°F (175°C).
Bake for 40-50 minutes, or until the casserole is golden brown and set in the center. A knife inserted into the center should come out clean.
Let it cool slightly before serving. Serve warm with your favorite toppings like maple syrup, powdered sugar, or fresh fruit.
Notes
This French toast casserole is incredibly versatile. You can add berries or chocolate chips to the mixture before baking for extra flavor. For a crisper top, you can uncover it for the last 10-15 minutes of baking.