Banana Layer Cake With Mascarpone Frosting

Name: Banana Layer Cake With Mascarpone Frosting
Ingredients: 1 1/2 cups all-purpose flour; 3/4 teaspoon baking powder; 3/4 teaspoon baking soda; Scant 1/2 teaspoon salt; 1 stick (4 ounces) unsalted butter, softened; 3/4 cup granulated sugar; 2 large egg yolks; 1 teaspoon pure vanilla extract; 3/4 cup mashed ripe banana (1 1/2 large), plus 2 large bananas, thinly sliced; 1/4 cup plus 2 tablespoons buttermilk; 3 large egg whites; 1 1/2 cups chilled mascarpone (12 ounces); 1 3/4 cups confectioners' sugar