Split and scrape out vanilla seeds from the pod and add it to milk in the saucepan and bring to a boil.
Meanwhile, in a mixing bowl add sugar, cornflour and egg yolks and mix together until combined1.
Once the milk has come to a boil, temper the egg yolks by pouring milk in a little at a time, continuously stirring until about half the liquid has incorporated.
Add it back into the pan with the remaining milk.
Over a low to medium heat keep stirring with a spatula making sure to scrape the bottom and sides of the pan. It will start to thicken, as it thickens keep stirring for 2-3 minutes to cook out the cornflour.
Take off the heat and add in the butter, mix vigorously to completely emulsify the butter2.
Pass through a fine mess sieve to remove any strands of the vanilla pod and eggy lumps.
Place the crème patisserie int a container, surface wrapped with cling film and into the fridge for around 4 hours to set up.
Once it is set and you are ready to use, take it out of the fridge and leave it no your work bench for 15 minutes to take the chill off it.
Place into your stand mixer bowl or mixing bowl and whisk until it is smooth and lump free (around 2 minutes).
You now have perfect crème patisserie to pipe and fill your creations.
