Taste Chocolate Mud Cake

mudcake Chocolate – what went wrong with the filling?
I have a recipe for chocolate mud cake that knows great, but the filling did not set.
Has cream, chocolate, egg yolks and powdered sugar (super fine sugar). I followed the instructions – melted chocolate into the cream, whisk the egg yolks and sugar in a bowl of hot water for 5-6 minutes, until pale and creamy, then beat him again for another 5-6 minutes when the mixture of chocolate is added. I stopped a few times while I was doing – Could have been the problem? Or was it because I was not able to use it until the next day? Any ideas? The cake and the ganache (bitumen) on the outside were good – but the recipe calls for filling is sandwiched between two layers of cake and chilled the whole thing – it's just that filling did not set – although great taste
Cooked egg yolks did not get enough. In this recipe cooked yolks to get sugar.
Beat the egg yolks with the longer and sugar over hot water.
Taste More Birthdays/ Alexandra Mudry