Mix the chocolate or cocoa in the boiling milk and sweeten to taste. When nearly cold add to this the yolks, well beaten, and the heavy cream. Mix thoroughly and strain into china cases. Place these in a large shallow stewpan containing just sufficient water to reach half way up on the cases. Let steam for twenty minutes, when the custard ought to be firm. The water should be boiling when the cases are first put in, but afterwards may simmer. Put the cases on ice, and serve as cold as possible with little sponge cakes or lady fingers.