This recipe is an adaptation of one given me by Peggy Pinckley, owner of the now-defunct Parisian Pantry in Springfield, Missouri, and a native of Scotland.
Set racks at the middle and upper thirds of the oven and preheat to 325 degrees.
Beat the butter in a mixer with a paddle until soft and light. Beat the sugar in a stream and continue beating for 5 to 10 minutes, until the mixture is very light and pal