You could use chocolate ice cream instead for extra chocolaty shake. Since someone gave me a low rating because this shake was not as thick as they wanted, I will specify that this recipe is not meant to make a super thick shake. If that's what you're after, combine the rest of the ingredients first and then slowly add the milk as you mix until you get to the consistency you want; probably it will end up somewhere between 1/4 and 1/2 cup milk for a fairly thick shake and may be as little as 1/8 of a cup or less if you want it so thick that you couldn't suck it up through a straw.