Dark Chocolate Cupcakes

For the cupcakes: 

Preheat the oven to 350 degrees. Line a 12-cup cupcake pan with paper liners.

In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt. In a small bowl, stir together the buttermilk and vanilla.

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and both sugars on medium-high speed until light and fluffy, 2 to 3 minutes. Reduce the speed to medium-low, add the eggs one at a time, and beat until creamy, 1 to 2 minutes. Slowly add half the flour mixture, then the buttermilk mixture, then the remaining flour mixture, beating until just blended after each addition. 

Divide the batter evenly among the liners and bake until the tops are just dry to the touch and a toothpick inserted into the center comes out clean, 18 to 20 minutes. Transfer the pan to a wire rack and cool completely before frosting with dark chocolate frosting.

For the Dark Chocolate Frosting: 

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and salt on medium speed until fluffy, 1 to 2 minutes. Gradually add the confectioners sugar and beat until smooth, 2 to 3 minutes. Add the vanilla and melted chocolate and beat until just incorporated, being careful not to incorporate too much air into the frosting. Add milk 1 tablespoon at a time, if needed, to achieve a spreadable consistency.