Allow butter and eggs to stand at room temperature for 30 minutes. Meanwhile, line twenty-four 2-1/2-inch muffin cups with paper bake cups. In a medium bowl stir together flour, baking powder, salt, and baking soda. In a small bowl combine mashed banana, milk, sour cream, and vanilla. Set aside.
Preheat oven to 350 degrees F. In a large mixing bowl beat butter with an electric mixer on low to medium speed for 30 seconds. Gradually add sugar, about 1/4 cup at a time, beating on medium speed until light and fluffy, scraping sides of bowl. Add eggs, one at a time, beating well after each addition. Alternately add flour mixture and banana mixture to butter mixture, beating on low speed after each addition just until combined.
Spoon batter into prepared muffin cups, filling each one-half to two-thirds full. Use the back of a spoon to smooth out batter in muffin cups.
Bake for 18 to 20 minutes or until a toothpick inserted in centers comes out clean. Cool cupcakes in muffin cups on wire racks for 5 minutes. Remove cupcakes from muffin cups. Cool completely on wire racks.
Just before serving, place some of the Sweetened Whipped Cream in a pastry bag fitted with a large star tip. Insert tip into the top of each cupcake. Squeeze about 1 tablespoon of the whipped cream into the center of each cupcake.
For each serving, top a cupcake with a small scoop of ice cream. Drizzle with chocolate-flavor syrup. Pipe some of the remaining Sweetened Whipped Cream on top of ice cream. Top with maraschino cherries and/or nuts. Makes 24 (2-1/2-inch) cupcakes.
Sweetened Whipped Cream
In a chilled mixing bowl combine whipping cream, sugar, and vanilla. Beat with an electric mixer on medium speed until soft peaks form (tips curl).