Cut 1/4 cup cold butter into the flour mixture. You can do this with a pastry cutter
(my preferred method) or using a fork. You can also use a cheese grater to grate the butter, then mix it together with a fork. However you do it, just make sure you are cutting the dough and not mixing it. You want to have individual pieces of flour-coated butter, with chunks up to the size of a pea. See photo.