Set up a double boiler with a pot of water and a stainless steel bowl. The water level should not touch the bottom of the bowl.
In stainless steel bowl whisk yolks and sugar until mixture turns pale yellow and ribbony (approximately three minutes). Whisk in liquor and place bowl over simmering water. Whisk vigorously over the water for 10 to 15 minutes until mixture triples in volume and reaches 140 degrees on thermometer. The egg will froth at first, and then stiffen. If the eggs start to scramble, remove from heat and whisk harder. Return to heat, continue. Cool mixture and serve with berries and cream.
Notes
*Marsala is traditionally used. I like Grand Marnier for berries, and occasionally even champagne. Be adventurous. Try different liqueurs or spirits. The ingredient may change, but the technique remains the same.