Preheat your oven to 180°C/350°F.
First, cream together the butter, powdered sugar and vanilla.
It doesn't take very long at all.
Then add in the flour and custard powder.
I used an ice cream scoop to ensure everything was even but you could roll them into a ball with you palms and them press it slightly with you index and middle finger.
Then use a fork and press it down a little. And don't worry if yours breaks or anything, it's supposed to look like this. I actually prefer the rustic look compared to the prim and proper ones. :)
Bake it for 18-22 minutes and you're done!