Mix the flour and cornstarch together. Put the egg yolks and sugar into a bowl and whisk until it turns pale.

Sieve Step 1 into a bowl and mix well.

Put the milk in a saucepan and put on a medium heat. Take it off the heat just before it starts to boil, and add to Step 2 little by little.

Strain through a fine mesh strainer back into the saucepan, and heat whilst stirring with a wooden spoon.

Turn off the heat once it turns into the consistency of cream. Add the butter and vanilla essence, and mix well.

Pour the custard cream into a shallow tray and let it cool. Wrap with cling film and chill in the fridge.