This one appears to be a disaster, but I've not used all of it, and I will try again this weekend.
25g powdered sugar
1 egg yolk
150g or 1 1/4 cup pastry flour
pinch of salt
Cream the butter until smear-able, but not light and fluffy--we are not making cookies here. Add the powdered sugar and salt. Add the egg yolk.
Mix in the flour. Do Not Overmix, because I think I overmixed which is why it's not so good.