Creating The Best Blueberry French Toast Casserole is straightforward when you follow these simple steps:

1. Prep the Bread: Cut the day-old French bread into 1-inch cubes and place them into a greased 9×13-inch baking dish. Spread the blueberries evenly over the bread.
2. Mix the Custard: In a large mixing bowl, whisk together the eggs, whole milk, heavy cream, granulated sugar, vanilla extract, ground cinnamon, and salt until well blended.
3. Combine: Pour the custard mixture evenly over the bread and blueberries, ensuring that all pieces are soaked.
4. Chill: Cover the dish tightly with plastic wrap and refrigerate for at least 4 hours or overnight. This allows the bread to absorb the custard fully.
5. Preheat the Oven: When ready to bake, preheat your oven to 350°F (175°C).
6. Bake: Remove the plastic wrap and bake uncovered for 45-55 minutes, or until the casserole is set and golden brown on top.
7. Check for Doneness: Insert a knife into the center; if it comes out clean, the casserole is done. If not, bake for an additional 5-10 minutes.
8. Cool: Once baked, remove the dish from the oven and let it cool for about 10 minutes before serving.
9. Serve: Dust with powdered sugar before serving for a delightful finishing touch.

These step-by-step instructions will guide you to create an incredible dish that impresses both family and friends.