First off you can use any of the Brewing cocoas. Combine a couple heaping tablespoons in a pint of cold water, give it a shake and let it set for a day, then strain it off.  It could hardly be simpler.

I have an Italian espresso maker with individual control of brew temp and pressure and I would like to start making "mocha" shots, 50/50 coffee/cocao. Any suggestions on a particular bean, grind, proportion, or technique to get started.