For the cupcakes: Preheat the oven to 350 F. Line a 12-cup standard muffin tin with paper cupcake liners.

In a medium bowl, combine the flour, baking powder, baking soda and salt. Set aside.

In a large bowl, add the butter and granulated sugar. Beat with a handheld mixer until combined. Add the sour cream and vanilla. Slowly beat in the eggs, one at a time. Incorporate the dry mixture and wet mixture together until thoroughly combined. Add the bananas and 1/2 cup walnuts, being careful not to overmix.

Using an ice cream scoop, fill each cupcake liner three-quarters of the way full. Bake in the oven until the tops turn golden brown and a toothpick inserted in the middle of the cupcake comes out clean, 18 to 20 minutes. Remove the cupcakes from the oven to a wire rack and let cool before frosting.

For the frosting: In a large bowl, add the cream cheese and butter. Beat together until incorporated. Add the molasses and mix well. Stir in the confectioners' sugar, milk and vanilla.

To assemble: Heavily frost the cupcakes and garnish with the remaining 1/4 cup walnuts.