You need to first boil the cream and milk in a large saucepan on the stove.
While that is cooking, you can be whisking together your egg yolks, cornflour, vanilla, sugar.
Once your milk is boiling, you can pour that into the sugar and egg mixture.
From there, clean out the saucepan and put the entire mixture back into it on the stove.
Using a wooden spoon to stir, heat the mixture on a low heat.
Be sure to stir thoroughly and heat evenly and keep stirring until the mixture has thickened. Don’t mix too long or lumps will begin to form.