In a medium-sized mixing bowl beat the egg yolks with the sugar replacement until light and fluffy.
Heat milk just to boiling.
Pour hot milk over egg yolk mixture, beating constantly.
Beat in melted chocolate.
Return mixture to saucepan.
Cook and stir over low heat until mixture thickens.
Remove from heat and cool.
Beat slightly with electric mixture to loosen.
Fold prepared nondairy whipped topping into custard.
Chill or freeze.