Prepare a 9x13 baking pan by spraying it with cooking spray. Set aside.
Cut or break up the French bread into small 1-inch pieces and arrange bread as a bottom layer on the baking pan.
Using a tablespoon measuring spoon, scoop out the Mascarpone cheese and place the dollops evenly over the bread layer.
Sprinkle one cup of the blueberries evenly over the mascarpone cheese and cubed bread. Set aside.
Mix together the eggs, half and half, honey, vanilla, cinnamon, and nutmeg in a large bowl. Pour the mixture into the baking pan, making sure to cover all of the bread. Cover the baking pan and let it sit in the refrigerator overnight.
The next morning, preheat the oven to 350℉ and bake the casserole covered in aluminum foil for 25 minutes and then uncovered for another 30 minutes, or until bubbly.
Drizzle the blueberry syrup over the casserole when it comes out of the oven.