Sift the confectioners’ sugar, salt, cocoa and espresso powder into a bowl.
Whip the butter for about 5 minutes using a paddle attachment (in a standing mixer).
Beat in the sugar mixture slowly.
Add vanilla and drizzle in the cream while beating until desired consistency is reached. If the you want the buttercream to have a stronger espresso taste, add as much as you would like!
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Notes
Sift the cocoa powder, and powdered sugar before adding to the butter. Both can hav lumps that will clog piping tips and disturb the consistency.
If your buttercream has a grainy texture add a tablespoon of cream and mix. Keep adding cream, or coffee if desired while mixing until the consistency is to your satisfaction.
If possible, use a high-quality Dutch processed cocoa powder.
Don't have unsalted butter on hand? Use salted butter and skip that 1/2 tsp. You can add additional salt to taste at the end if needed.