Generously grease a 9x13 inch baking dish with melted butter.

Cut the bread into one-inch cubes and spread half of them into the bottom of the prepared dish.

Sprinkle half of the blueberries over the bread. Repeat with the remaining bread and blueberries.

In a large bowl, whisk together the eggs, milk, heavy cream, sugar, vanilla extract, and cinnamon.

Slowly pour the custard mixture over the bread cubes. Use a spatula to gently press down on the bread, ensuring every piece is submerged or coated.

Cover the dish with foil and let it sit in the fridge for at least 3 hours, or ideally, overnight.

Preheat the oven to 350 degrees Fahrenheit. Bake covered for 30 minutes, then remove the foil and bake for another 20 to 30 minutes.

Let it stand for 10 minutes before serving. Dust with powdered sugar and serve with warm maple syrup.