In the top of a double boiler or in a metal bowl, combine the yolks, sugar, and liqueur until smooth. Set over a pot of barely simmering water and whisk by hand or beat with an electric mixer until pale yellow and foamy and a ribbon forms when the beaters are lifted, 5 to 7 minutes.
Remove from the heat and beat in the cocoa until smooth.
Recipe courtesy Emeril Lagasse, 2004
Recipe courtesy of Dave Lieberman