Mix together butter and sugar until smooth. Stir in cocoa powder, vanilla, coffee (or milk), and oats. Let the batter cool in the fridge for 15 minutes so it's easier to roll.
Pour coconut (or other topping) into a shallow bowl. Roll tablespoons of the cookie dough into balls with your hands. Gently roll each ball in the coconut. Set on a plate. Refrigerate until firm, at least 15 minutes. Serve chilled.