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1
Make cupcakes: Preheat oven to 375F.
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2
Line standard muffin tins with paper liners.
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3
Whisk together flour, baking soda, baking powder, and salt.
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4
With an electric mixer on medium-high speed, cream butter and granulated sugar until pale and fluffy.
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5
Reduce speed to low.
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6
Beat in peanut butter until combined.
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7
Add eggs, one at a time, beating until each is incorporated, scraping down sides of bowl as needed.
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8
Beat in vanilla.
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Add flour mixture, and mix until just combined.
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10
Beat in sour cream.
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11
Fill each lined cup with 3 scant tablespoons batter.
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12
Bake, rotating tins halfway through, until pale golden and a cake tester inserted in centers comes out clean, about 13 minutes.
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13
Transfer tins to wire racks to cool completely before removing cupcakes.
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14
Make frosting: With an electric mixer on medium-high speed, beat cream cheese, confectioners sugar, and butter until pale and fluffy.
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15
Stir in peanut butter by hand.
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16
To finish, use an offset spatula to spread 1 to 2 tablespoons frosting onto each cupcake.
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17
Refrigerate until frosting is firm, about 10 minutes.
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18
Score each top in a crosshatch pattern with the tines of a fork, dipping tines in confectioners sugar each time to prevent sticking.
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19
Cupcakes can be refrigerated up to 2 days in airtight containers; bring to room temperature before serving.
