in a double boiler over low heat. Once melted, whisk in 1.25 cups
sugar until dissolved, then whisk in butter. When everything is
well incorporated, remove from heat and whisk in liqueur. Whip
egg yolks until light in color.
Gradually whip chocolate mixture into yolks. Whip egg whites in
a separate bowl until foamy, add ¼ cup sugar and whip until
stiff peaked. Fold egg whites into chocolate mixture until smooth.
Pour batter into buttered/floured spring form pan (12”).
Steam bake for 3 hours at 275. Let cool in oven. Remove from oven,
invert and release springform. Serve with vanilla sauce.