Chocolate Peanut Butter Cupcakes with Peanut Butter Frosting

I know its Cinco de Mayo and I should be sharing a festive recipe today, but these cupcakes took priority!  I had the honor and privilege of baking cupcakes for my roommate's boss' birthday (got that?).  After sifting through many cake and cupcake recipes -- I decided on these.  I was nervous because they sound very rich but I thought they turned out perfect!
  

The center is like a buckeye (awesome) and the chocolate cake was just right.  This could be my new go-to peanut butter frosting.  I'm thinking it would be perfect with banana cupcakes.  The chopped peanuts were my own addition (and totally optional) but I thought they added great flavor.
AND as for Cinco de Mayo -- I will be celebrating this evening.
Chocolate Peanut Butter Cupcakes
Source:  Dinner & Dessert

For the filling:
1 cup confectioners’ sugar
¾ cup creamy peanut butter
4 tbsp. unsalted butter, at room temperature
½ tsp. vanilla extract

For the cake:
1 2/3 cups all-purpose flour
¾ cup unsweetened cocoa powder
1 tsp. baking soda
½ tsp. salt
1 cup sour cream
2 tbsp. milk
1 tsp. vanilla extract
8 tbsp. unsalted butter, at room temperature
1½ cups sugar
2 large eggs

Directions:
Preheat the oven to 350° F.  Line two cupcake pans with paper liners.

To make the filling, combine the confectioners’ sugar, peanut butter, butter and vanilla extract in a bowl.  Beat with an electric mixer on medium speed until well combined.  Roll the mixture into 1-inch balls (at least 24) and set aside on a baking sheet.

To make the cake batter, combine the flour, cocoa powder, baking soda and salt in a medium bowl; whisk together and set aside.  In a liquid measuring cup, stir together the sour cream, milk and vanilla extract.  In the bowl of an electric mixer fitted with the paddle attachment, combine the butter and sugar, and beat on medium-high speed until light and fluffy, about 2 minutes.  Beat in the eggs one at a time, scraping down the bowl as needed.  With the mixer on low speed, alternately add the dry ingredients and the sour cream mixture, beginning and ending with the dry ingredients.  Mix just until incorporated.

Spoon a tablespoon or two of batter into the bottom of each cupcake liner.  Place a ball of the peanut butter filling in each cupcake well and top with the remaining batter so that all the cups are filled.  Bake for 18-22 minutes, or until a toothpick inserted in the center comes out clean.  Allow to cool in the pan for 5-10 minutes, then transfer to a wire rack to cool completely.

Frosting
1 cup confectioners’ sugar
1 cup creamy peanut butter
5 tablespoons unsalted butter, at room temperature
3/4 teaspoon pure vanilla extract
1/4 teaspoon kosher salt
1/3 cup heavy cream

Place the confectioners’ sugar, peanut butter, butter, vanilla, and salt in the bowl of an electric mixer fitted with a paddle attachment. Mix on medium-low speed until creamy, scraping down the bowl with a rubber spatula as you work. Add the cream and beat on high speed until the mixture is light and smooth.