Whip the heavy whipping cream until it firmly holds peaks. Set aside in the refrigerator.
Whisk the eggs and sugar until very fluffy and thick - about 10 minutes on high speed in a stand mixer.
Mix the butter into the melted chocolate until it is all melted.
Add the chocolate mixture into the sugar/butter mixture, then fold in the whipped cream.
Pipe onto a variety of cakes and desserts. Goes great with chocolate and vanilla cupcakes!