Banana Cupcakes with Peanut Butter Frosting

Preheat the oven to 350 degrees F (175 degrees C). Line a 12-cup muffin pan with paper liners.

Whisk flour, baking powder, baking soda, and salt together in a medium bowl. Mash bananas with a fork in another medium bowl until smooth. Mix sour cream and vanilla extract into bananas.

Combine sugar and butter in a large bowl; beat with an electric mixer until light and fluffy, about 3 minutes. Add egg and egg yolk and beat until well blended. Add flour mixture in 2 batches, alternating with banana mixture, beating batter briefly after each addition until just blended. Scoop batter into the prepared muffin cups, adding about a generous 1/4 cup in each.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 20 minutes. Cool in the tin for 5 minutes. Transfer to a wire rack to cool completely, about 20 minutes.

Meanwhile, sift powdered sugar into a large bowl. Add cream cheese, butter, and peanut butter; beat with an electric mixer until smooth. Spread or pipe frosting onto the cooled cupcakes.