You will need a stand mixer or a mixing bowl for this step. Add the butter, a cup of cocoa powder, and 2 teaspoons of vanilla extract and then mix everything well to combine. Then, add the powdered sugar to the mixing bowl, one cup at a time. Be sure to mix thoroughly between each addition. “Don’t forget to sieve the cocoa powder and the powdered sugar so you end up with lovely smooth buttercream,” Bryant notes.
Next, you can add ¼ cup of brewed coffee. If the mixture is still pretty stiff, you can add a little milk until the buttercream reaches a smooth and silky consistency. Then, put any unused milk back in the fridge. “It’s important to keep an eye on the texture of the buttercream when adding the coffee and then the milk. It needs to be smooth and spreadable, you don’t want it too runny, else it will drip off the cake, or too thick, else it won’t spread well,” Bryant adds.