In a large bowl sift together the powdered sugar and cocoa to remove any lumps. Set aside.

Place the room temperature butter in a stand mixer fitted with the whisk attachment. Beat on high speed until fluffy and pale in color, roughly 2-3 minutes.

Turn the machine down to medium-low speed and slowly add the powdered sugar, 1 tablespoon at a time until fully incorporated.

Scrape down the bowl and add the vanilla, salt, espresso, and 3 tablespoons of milk. Beat on high speed for roughly 3 minutes until light and fluffy. Add the extra tablespoon of milk if you want a thinner frosting.

Your frosting is ready to decorate or you can put it in the fridge to firm up for a minimum of 30 minutes but up to 5 days. Allow to sit out at room temperature for 1 hour before using.