Step 1

Preheat the oven to 350 degrees F. Line a muffin pan with 12 cupcake liners.

Step 2

** I like to mix the chocolate batter and the peanut butter batter at the same time (in different bowls) to make it quicker. **

Step 3

In 2 small mixing bowls (remember which is chocolate and which is peanut butter) measure the appropriate amount of flour, baking soda, baking powder and salt into each. Add cocoa powder to the chocolate bowl. Gently mix each bowl with a spoon. Set aside.

Step 4

In 2 larger mixing bowls (remember which is chocolate and which is peanut butter) add the room temperate butter and sugar to the chocolate bowl and add creamy peanut butter, vegetable oil and sugar to the PB bowl. Mix each with an electric mixer on medium speed for 30 seconds. I quickly rinse the beaters in-between.

Step 5

Next add the egg, vanilla, sour cream and melted chocolate to the chocolate bowl, beat with the mixer until combined. Rinse the beaters and add the egg, vanilla, sour cream, and milk to the PB bowl. Beat with the mixer until combined.

Step 6

Gradually spoon the chocolate flour mixture into the chocolate bowl and use a spatula to mix by hand just until no flour clumps remain.

Step 7

Repeat with the peanut butter flour mixture for the peanut butter bowl, but be sure to add in the chopped peanut butter cups too, mixing by hand with a spatula, just until no flour clumps remain.

Step 8

Use a cookie dough scoop to add one scoop of each batter to each muffin cup. The batter will be THICK. The cups should be fairly full. Swirl the batter together with a butter knife if desired.

Step 9

Bake for 18-21 minutes or until a toothpick inserted in the center comes out clean.

Step 10

Allow the cupcakes to cool for 7 minutes in the pan, then remove them from the pan and allow them to cool completely.

Step 11

Place room temperature unsalted butter in a mixing bowl. Use an electric mixer on medium and beat the butter for 1 minute, until whipped and fluffy.

Step 12

Add in the cocoa powder, powdered sugar and vanilla extract, beat again on low for 1-2 minutes, scraping down the sides of the bowl, until everything is incorporated.

Step 13

If the frosting is too thick, add a tablespoon of milk or heavy cream, and beat until creamy.

Step 14

Place room temperature unsalted butter and creamy peanut butter in a mixing bowl. Use an electric mixer on medium and beat the butter for 1 minute, until whipped and fluffy.

Step 15

Add in the powdered sugar and vanilla extract, beat again on low for 1-2 minutes, scraping down the sides of the bowl, until everything is incorporated.

Step 16

If the frosting is too thick, add a tablespoon of milk or heavy cream, and beat until creamy.