Combine butter and cocoa in the bowl of a stand mixer (or in a large bowl with an electric hand mixer) fitted with a whisk attachment. Start on low speed until incorporated and then whip on medium until completely combined. Add iced coffee. Whip until combined. Reduce speed to low. Add powdered sugar, one cup at a time until combined.
Whisk on high for 2-3 minutes until frosting becomes light and fluffy and lightens in color.
Use to frost cakes, cupcakes, brownies, or eat with a spoon. I won't judge.
Notes
This recipe will frost a 9-inch (2 layer cake) or a 9x13 cake (with left overs to spare). For 24 cupcakes or a single 8 or 9-inch square cake, halve the recipe.If the frosting is a little sweet for your palate, add a pinch of table salt to help take the edge off the sweet. The salt will not make it salty, just balance the sweetness.If your powdered sugar or cocoa are lumpy, give them a stir with a fork to break up the lumps before adding to the mixer, this will result in a smoother frosting.