Mix your base.
Bring 1 cup of milk to a gentle simmer.
Stir the hot milk into the egg mixture.
Pour the mixture back into the saucepan and heat it.
Chill the custard. Pour it into a bowl, cover it, and chill it in the refrigerator until it's completely cool.
Add 1 cup heavy cream and mix-ins. Finish the base by adding a cup of heavy cream and stirring well