Preheat oven to 350°F. Line a standard cupcake pan with 7 paper liners.

In the bowl of a stand mixer, cream together butter and sugar. Mix in egg and vanilla, followed by salt and baking soda. Scrape bowl as needed. Mix in cocoa powder. Increase speed, mixing until fully combined. Add in sour cream, followed by flour. Mix until no streaks remain. Lastly, slowly add in coffee. Mix until just combined. 

Using a large cookie scoop, divide batter equally between prepared liners. Bake for 18-20 minutes. Cool in pan for several minutes or until easy to handle. Transfer to a cooling rack to cool completely. 

Prepare frosting in a large bowl or stand mixer, fit with the paddle attachement. Beat together butter and shortening until smooth and fully combined. Mix in peppermint, followed by 1 cup of powdered sugar at a time. Mix completely between additions. Add in enough heavy cream until desired consistency is reached. 

Prepare a large piping bag with a jumbo open tip. 

Optional candy cane striping: Using a clean paint brush, add four thin stripes of red food gel to the inside of the bag. Carefully add prepared frosting to the bag. Pipe onto cooled cupcakes.