Preheat oven to 350 degrees F. Add cupcake liners to a 12 serving cupcake pan, and set aside.

In a small mixing bowl, whisk together flour, baking powder, and baking soda. Set aside.

Combine vanilla extract with milk. Set aside.

Add butter to a large mixing bowl, and beat with an electric mixer until creamy.

Add brown sugar and eggs to butter and mix until well combined.

Scrape sides of bowl with a rubber spatula and mix again to ensure all ingredients are well combined.

Add sour cream and peanut butter to the bowl. Beat until smooth.

With the mixer set on low speed, gradually pour in milk and dry ingredients and mix until well combined.

Increase mixer speed and beat until batter becomes smooth and fluffy.

Using a large spoon, divide batter evenly into prepared cupcake pan, filling about ¾ full.

Bake on 350 F. for 17-18 minutes, or until a toothpick inserted in the center comes out clean.

Place each cupcake on a wire cooling rack to cool.

Add butter to the bowl of an electric mixer and beat for about 1 minute, or until very creamy.

Slowly add in powdered sugar and vanilla, and mix until well combined.

Slowly add in a small amount of milk until desired consistency is reached.

Reserve approximately ¼ cup of frosting in a piping bag fitted with a small round tip. This will be used for football stitches.

Add cocoa powder and chocolate pieces to remaining frosting and beat until smooth.

Add chocolate frosting to a large piping bag fitted with a large round tip, and pipe a swirl onto each cupcake.

Use white frosting to pipe on a simple football stitch pattern.