Grease a 2- to 2 1/2-quart baking dish. Arrange half of the bread slices in the dish, overlapping as necessary. For filling: In a small bowl whisk together mascarpone, 1/4 cup of the nut butter, and 1/4 cup of the maple syrup until smooth. Spoon evenly over bread in dish. Slice two of the bananas crosswise. Layer over filling. Arrange remaining bread over filling.

In a large bowl whisk together eggs, milk, 1/4 cup of the remaining maple syrup, the vanilla, and cinnamon. Slowly pour egg mixture over bread, pressing down bread as you pour. Chill, covered, 2 to 24 hours.

Preheat oven to 375°F. Bake, uncovered, 50 to 65 minutes or until center is set (at least 180°F), covering with foil halfway through baking. Let stand 15 minutes.

Meanwhile, bias-slice remaining two bananas. In a large skillet heat the butter, the remaining 1/4 cup maple syrup, and remaining 1 tablespoon nut butter over medium until bubbly. Add banana slices. Cook 2 minutes or until thickened, stirring occasionally. Spoon warm banana mixture over dish. Serves 8.