Preheat the oven to 350°F. Line cupcake tins with liners.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar until light and fluffy, about 3 minutes, scraping down the sides as needed. Add the eggs one at a time, beating between each addition, then add the vanilla extract.
In a small bowl, whisk together the buttermilk and sour cream.
In a separate medium bowl, whisk together the flour, cocoa powder, baking soda and salt.
Alternately add the buttermilk mixture and flour mixture to the stand mixer in three increments each, beating between each addition. (Do not overmix the batter.)
Fill the cupcake tins about 2/3 full then bake the cupcakes for 15 to 18 minutes until a toothpick inserted comes out clean. Cool the cupcakes in the pan for 10 minutes then transfer them to a rack to cool completely while you make the frosting and decorations.