Preheat the oven to 350º F. Line a muffin tin with 12 cupcake liners.

In a small mixing bowl, combine the cocoa powder, flour, baking powder, baking soda and salt. Gently mix using a spoon.

In a larger mixing bowl, combine the butter and sugar, beat using an electric mixer until fluffy. Add in the eggs and vanilla, lightly beat.

Add in the sour cream and melted chocolate, mix by hand using a spatula.

Add half of the flour mixture to the wet ingredients, do not dump it in, rather take spoonfuls of the flour mixture and gently shake it over the wet ingredients, as if you were sifting in the flour. Fold in the mixture until no flour remains. Repeat with the other half of the flour, folding it in and scraping the sides and bottom of the bowl to incorporate everything. Set aside.

In a bowl combine the flour, baking soda, baking powder, and salt. In a separate bowl, combine the peanut butter, oil, and brown sugar, beat together using an electric mixer. Add in the egg and vanilla, beat again. Add the flour mixture and buttermilk, alternating between the two and mixing by hand until everything is incorporated.

Begin to add the batter into the pan, alternating between chocolate and peanut butter. Fill the cupcake liners almost completely full with batter.

Place the pan in the middle of the oven and bake for 15-17 minutes or until a toothpick inserted in the center comes out clean.

Allow the cupcakes to cool for about 3 minutes in the pan, then take them out and allow them to cool upside down on a cooling rack. This will help create cupcakes with a dome top.

Allow the cupcakes to cool completely before adding the frosting.

In a mixing bowl, combine the butter and vegetable shortening, beat using an electric mixer until fluffy. Add in the cocoa powder, and gently mix by hand with a spatula.

Begin to add the powdered sugar, 1 cup at a time, mixing by hand first, then with the electric mixer. Continue adding powdered sugar until the frosting tastes good to you.

In a mixing large bowl, combine the butter and vegetable shortening, beat using an electric mixer until fluffy.

Add in the peanut butter, beat using electric mixer.

Begin to add the powdered sugar, 1 cup at a time, mixing by hand first, then with the electric mixer. Continue adding powdered sugar until the frosting tastes good to you.

In a piping bag fit with a wilton 6B piping tip, do your best to add chocolate buttercream to one side of the bag and peanut butter buttercream to the other. Push the buttercream down into the bag. Pipe the buttercream onto the cupcakes, starting on the outside edge and working your way into the center, progressively stacking the frosting as you get to the center.