Creating the Best Blueberry French Toast Casserole is simple when following these steps:

1. Prep the Baking Dish: Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish with butter.
2. Prepare the Bread: Cut the French bread into 1-inch cubes and place half of them in the prepared baking dish.
3. Add Blueberries: Scatter half of the blueberries evenly over the bread cubes.
4. Layer the Remaining Bread: Top with the remaining bread cubes and blueberries, ensuring an even distribution.
5. Mix the Custard: In a large bowl, whisk together the eggs, milk, heavy cream, sugar, vanilla extract, cinnamon, and salt until well combined.
6. Combine with Bread: Pour the egg mixture over the bread and blueberries. Press down gently to soak the bread evenly.
7. Let it Rest: Cover the dish with plastic wrap and allow it to sit for at least 30 minutes or up to 1 hour, allowing the bread to absorb the custard.
8. Bake: Remove the cover and bake in the preheated oven for 40-45 minutes, or until the top is golden brown and set in the center.
9. Cool Slightly: Once baked, remove from the oven and let it cool for about 5-10 minutes before serving.

By following these steps, you can create an incredible breakfast casserole that will leave everyone asking for seconds!