Stir in butter and sugar. Stir until sugar is dissolved, add flour and stir again.
Now knead this dough well and make it into a long roll.
Now put some sugar in the tray and roll this dough over and spread the sugar everywhere.
Carefully wrap it in cling wrap or a lunch sheet and leave it in the freezer for 30 minutes.
Loosen the cling wrap and cut it into slices. Place these slices in a baking tray and bake for 20 minutes in a preheated oven at 180.