Step 1

Preheat oven to 375°F. Line 2 or 3 standard 12-cup muffin tins with paper liners.

Step 2

In a medium bowl, whisk together the flour, baking powder, salt, and baking soda. In a separate bowl, use an electric mixer to combine the butter and sugar. Mix on medium speed until pale and fluffy. Reduce the speed to low. Mix in the peanut butter. Then mix in the eggs, one at a time, and then the vanilla. Add the flour mixture; mix until combined. And then mix in the sour cream.

Step 3

Spoon scant 3 tablespoons of batter into each muffin cup. Bake until pale golden and a toothpick inserted into the centers comes out clean, about 13 minutes. Transfer to wire racks; let cool completely.

Step 4

In a large bowl, use an electric mixer to combine the cream cheese, powdered sugar, and butter; mix on medium-high speed until pale and fluffy. Stir in the peanut butter with a rubber spatula.

Step 5

Spread 1½ tablespoons of frosting onto each cupcake. Refrigerate until the frosting is firm, about 10 minutes. Using the tines of a fork dipped in powdered sugar, score each cupcake top in a crosshatch pattern.

Step 6

Cupcakes can be refrigerated in single layers in airtight containers for up to 2 days.