Combine all the butter with all the caster sugar, in a bowl and wooden spoon.
Add the vanilla essence and egg yolk into the bowl and combine with the butter and caster sugar.
Then sift over 350g of flour into the bowl and mix until it becomes like dough, you may have to use your hands to get all the dough in one. If mixture is still sticky, add small amounts of flour until it's right. Preheat the oven to 200C.
You may have to give the dough some moisture so under a cold tap slightly moisten your hands and then roll the dough into a ball or a long sausage where you can cut them thinly and have circle biscuits.
Then after shaping them place them in the oven until they look slightly more than golden, dont worry they will change to a lighter colour and it will not affect the taste. You can eat them a couple of minutes after coming out of the oven.