In a greased 13x9-in. baking dish, layer bread cubes and blueberries. In a small bowl, beat mascarpone cheese and confectioners' sugar until smooth; drop by tablespoonfuls over blueberries. Top with bread slices.
In a large bowl, whisk eggs, cream, milk, granulated sugar and vanilla; pour over bread. Refrigerate, covered, overnight.
Preheat oven to 350°. Remove French toast from refrigerator while oven heats. Bake, covered, 30 minutes. Bake, uncovered, 30-40 minutes longer or until puffed and golden and a knife inserted in the center comes out clean.
Let stand 10 minutes before serving. Dust with additional confectioners' sugar; sprinkle with almonds. If desired, serve with additional blueberries.