Make the Cupcakes

1. Preheat oven to 350°F (176°C) and prepare a cupcake pan with cupcake liners.
2. Combine the flour, baking powder and salt in a medium sized bowl and set aside.
3. Add the butter and sugar to a large mixer bowl and beat together until light in color and fluffy, about 2-3 minutes. Do not skimp on the creaming time.
4. Add the eggs one at a time, mixing until well combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
5. Add half of the dry ingredients to the batter and mix until combined.
6. Add the sour cream and vanilla extract and mix until well combined.
7. Add the remaining dry ingredients and mix until well combined and smooth. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated. Do not over mix the batter.
8. Divide the batter in half in two separate bowls. If you have a food scale, I like to weigh the batter and then divide it in half evenly. Set one bowl aside. To the other bowl, add the melted chocolate and fold together to combine.
9. Drop alternating spoonfuls of each batter to the cupcake liners. You’ll need about 3 1/2 to 4 tablespoons of cake batter per cupcake.
10. Bake for 15-20 minutes, or until a toothpick inserted comes out clean.
11. Remove the cupcakes from the oven and allow to cool for about 2-3 minutes, then transfer to cooling racks to cool completely.

Make the Frostings & Assemble

1. When the cupcakes have cooled, make the buttercream. For the vanilla buttercream, add the butter to a large mixer bowl and beat until smooth.
2. Add about half of the powdered sugar and mix until smooth and well combined.
3. Add the vanilla extract, 1-2 tablespoons of the cream and the salt to the frosting and mix until well combined.
4. Add the remaining powdered sugar and mix until smooth. Add additional cream as needed to get the right consistency. Set buttercream aside.
5. To make the chocolate buttercream, add the butter to a large mixer bowl and beat until smooth.
6. Add about half of the powdered sugar and the cocoa powder and mix until smooth and well combined.
7. Add the vanilla extract, 1-2 tablespoons of the cream and the salt to the frosting and mix until well combined.
8. Add the remaining powdered sugar and mix until smooth. Add additional cream as needed to get the right consistency.
9. To create the swirl frosting, add the vanilla and chocolate buttercream to their own piping bags WITHOUT piping tips. I used 12 inch bags. You’ll then add both piping bags to a larger piping bag (I use a 16 inch bag) fitted with your piping tip (I used Ateco tip 847). The two smaller piping bags containing the buttercream frostings should be side by side in the larger bag.
10. Press the top of the large piping bag to squeeze the two buttercream frostings down into the piping tip and squeeze some out until you see both colors coming out, then pipe the buttercream onto the cupcakes.