First, mix cream, milk and boiled condensed milk in a saucepan. Put it on a stove and warm it. Place yolks in a bowl and stir well until smooth. Stir liquid ingredients when they will be warm enough, remove from the heat. Pour 200 grams in yolks and stir. After, add remaining mixture.
Place on a low heat again and constantly stir.
You have to get homogeneous creme mixture.