In a double boiler over simmering water, melt chocolate. Remove top pan from heat; stir in sugar and coffee. Add one yolk at a time, stirring until smooth. Place top pan over boiling water; cook and stir for 3-4 minutes or until thick. Pour into bowl; chill 6-8 minutes.
Fold in 3 cups whipped topping. Spoon into dishes. Top with whipped topping.