In a bowl, whisk egg yolks and sugar until completely mixed. Sit to the side.

In a medium saucepan over medium heat, add milk.

Heat the milk until it is scolding. Do not let it boil.

While whisking the eggs mixture constantly, slowly pour in milk. 

Pour mixture back into the saucepan and simmer for 3 minutes. Stir continuously.

Pour over your Irish Apple Cake.