In a double boiler over hot water, melt the chocolate chips with the confectioners’ sugar and butter. Remove from heat. Slowly stir a small amount of the melted chocolate into the egg yolks, then return this mixture to the melted chocolate in the double boiler and stir well. Blend in the vanilla, or the brandy or rum. Add the nuts, if desired. Chill without stirring for 1 to 2 hours. Combine grated chocolate and cinnamon on a plate. Form the chilled mixture into 1-inch balls and roll them in the grated chocolate and cinnamon. Store the truffles in the refrigerator in a covered container. Serve in small muffin papers or candy cups, or wrap in gold foil.