Preheat your oven to 350°F (175°C). Grease a baking dish.
In a mixing bowl, whisk together the eggs, milk, vanilla extract, maple syrup, ground cinnamon, and salt.
Layer half of the bread cubes in the baking dish. Scatter the blueberries and dollops of mascarpone cheese over the bread. Top with the remaining bread cubes.
Pour the egg mixture evenly over the bread. Press down lightly to ensure the bread absorbs the liquid.
Bake for 45 minutes or until the top is golden and the center is set. Let it cool for a few minutes before serving.
Serve with extra maple syrup if desired.
Notes:
For a richer flavor, you can use half-and-half instead of milk.