Grease a 9x13 inch baking dish and place half of the bread cubes in an even layer in the dish.
Sprinkle a layer of blueberries over the bread cubes.
In a large bowl, whisk together the eggs, milk, heavy cream, sugar, vanilla extract, cinnamon, and nutmeg.
Pour half of the egg mixture evenly over the bread and blueberries before adding the remaining bread cubes.
Add another layer of blueberries and pour the remaining egg mixture over the top evenly.
Cover the dish with foil and refrigerate for at least 2 hours or overnight for best results.
Preheat your oven to 350°F (175°C).
Remove the dish from the refrigerator and let it sit at room temperature for about 20 minutes.
Cover with foil and bake in the preheated oven for 30 minutes.
Remove the foil and continue baking for an additional 15 minutes, or until the top is golden and the casserole is set.
Let it cool for a few minutes before serving warm, optionally with a drizzle of maple syrup.