Dark Chocolate Cupcakes 

1. Preheat the oven to 350F(175C). Line (2) cupcake baking pans with 12-14 cupcake/muffin liners. Cupcakes may be baked in batches with (1) baking pan.
2. In a medium mixing bowl, add the flour, cocoa powder, baking powder, baking soda and salt. Whisk ingredients together to combine.
3. In the bowl of stand mixer fitted with paddle attachment or with a hand-held electric mixer and large mixing bowl, add the oil and sugar. Mix ingredients together at medium high speed to combine, about 1 minute.
4. Next, mix in the sour cream (or yogurt) into oil-sugar mixture to combine.
5. Beat the egg into wet batter at medium high speed until fully incorporated, about 30-60 seconds.
6. Reduce mixer speed to low. In an alternating fashion, starting and ending with the dry ingredients, mix half of the dry ingredients into wet batter followed by the coffee and vanilla extract and ending with the remaining dry ingredients.
7. Stop the mixer and use a rubber spatula to scrape the sides and base of the bowl to catch any unmixed ingredients.
8. Resume mixing chocolate cupcake batter at medium speed for an additional 30-60 seconds. The resulting batter should be slightly thick and smooth.
9. Equally divide cupcake batter into prepared baking pans.
10. Bake cupcake batter rotating the pan halfway through bake time for 16-18 minutes or until a toothpick inserted into the center of one of the cupcakes comes out clean.
11. Allow cupcakes to cool in the pan for 4-5 minutes before transferring to a cooling track to cool completely to room temperature. 

Chocolate Buttercream Frosting 

1. In the bowl of a stand mixer fitted with paddle attachment or with a hand-held electric mixer and large mixing bowl, cream the butter and salt at medium high speed until smooth and fluffy in appearance, about 2-3 minutes.
2. Reduce mixer speed to low and mix in 2 1/2 cups of the confectioners’ sugar and cocoa powder into creamed butter. Gradually increase mixer speed back to medium.
3. Once all the dry ingredients have been incorporated into creamed butter, mix in the vanilla extract and 2 1/2 tablespoons of heavy whipping cream into buttercream until fully incorporated.
4. If buttercream appears to be on the soft side, mix in the remaining confectioners’ sugar 1/4 cup at a time until a thick but pipeable consistency is reached.
5. If buttercream appears too thick, mix in remaining heavy whipping cream, 1/2 teaspoon at a time until the desired consistency (thick but pipeable) is reached.
6. Increase mixer speed to medium high and mix chocolate buttercream frosting for an additional 30-60 seconds. The resulting frosting should be smooth and fluffy in appearance.

Assembly 

1. Fill a large pastry bag fitted with desired pastry tip with chocolate buttercream frosting. I used a Wilton 8B pastry tip.
2. Pipe frosting on cooled cupcakes in a swirl design. Here is a video reference.
3. Top piped frosting with fresh blackberries and herbs of choice (optional) before serving.