Put chocolate, coffee, and sugar in a large metal mixing bowl. Set bowl over a large pot filled with 1 in. simmering water. Melt chocolate, stirring often, until smooth.
Remove from heat and set aside.
Whisk egg whites in a medium bowl with a mixer until they hold stiff peaks.
Whisk cream in another bowl until soft ribbons form.
Stir yolks into warm chocolate mixture.
Mix in liqueur. Using a rubber spatula, gently fold in whites until almost blended, then gently fold in whipped cream until no streaks remain.
Pour chocolate mixture into a large (8-cup) glass serving bowl. Cover bowl tightly with plastic wrap and chill until ready to serve.
