If not using chocolate chips, like a sensible person, chop chocolate and set aside. Heat the cream and butter in a small saucepan over medium heat. When butter has melted, add coffee. Bring to just shy of a boil. Turn off burner, and immediately pour the chocolate into the cream.
Alternately, put the above ingredients in a microwave-safe bowl and nuke them for a minute or two, not long enough to boil the cream, but enough to begin melting the chocolate.
Stir until smooth and consistently coloured. Cover and place in the refrigerator until the truffle mixture is firm (this will take several hours or overnight).
Sprinkle cocoa powder on a plate. Remove the truffle mixture from the refrigerator. With your hands, or else a melon baller or small spoon form the chocolate into round, bite-sized balls. Immediately roll the truffle in the coating and place on a parchment lined baking sheet or tray. Cover and place in the refrigerator until firm. Truffles can be refrigerated for a couple of weeks or else frozen for a couple of months. Bring to room temperature before serving.
Makes 30 small truffles.