Preheat the oven to 350°F (177°C). Line a 12-cup muffin pan with cupcake liners. Line a second pan with 2-3 liners because this recipe yields 14-15 cupcakes. Set aside.

Whisk the flour, baking soda, and salt together in a medium bowl. Set aside.

Using a handheld mixer, stand mixer fitted with a whisk or paddle attachment, or a whisk, mix the oil, peanut butter, brown sugar, egg, sour cream, and vanilla extract together in a large bowl. Add the dry ingredients, milk, and peanuts and whisk or beat together until completely combined. Avoid overmixing. Batter will be slightly thick.

Pour/spoon the batter into the liners, filling only 2/3 full to avoid baking over the sides. Bake for 21-23 minutes, or until a toothpick inserted in the center comes out clean and the tops of the cupcakes spring back when gently touched. For around 35 mini cupcakes, bake for about 11-13 minutes, same oven temperature. Allow the cupcakes to cool completely before frosting.

With a handheld or stand mixer fitted with a paddle or whisk attachment, beat the butter on medium speed until creamy, about 2 minutes. Add confectioners’ sugar, cocoa powder, and milk. Beat on low speed for 30 seconds, then add the peanut butter, vanilla extract, and salt. Beat on medium-high speed for 2 minutes until combined. Add 1/4 cup more confectioners’ sugar if frosting is too thin or another 1-2 Tablespoons of cream/milk if frosting is too thick. Taste. Add extra peanut butter or a pinch of salt if desired.

Frost cooled cupcakes. I piped a basic tall swirl using Ateco 849 piping tip. You can watch me decorate the cupcakes in the video in the blog post. Garnish with peanut butter cup, if desired.

Cover and store leftovers in the refrigerator for up to 5 days. I recommend a cupcake carrier for storing and transporting decorated cupcakes.