Set oven at 350 degrees. Beat the butter until smooth and creamy, add sugar and beat until fluffy. Mix the flour, baking powder and salt together, then add gradually to the butter mixture just until blended. Turn the dough out onto a floured board and roll out to 1/4 inch thick. Cut out into squares or with cookie cutters into heart shapes, etc. Prick each cookie with a fork. Bake on ungreased cookie sheets for 20-25 minutes until just barely brown on the edges.
Serve them as they are, a beautiful creamy golden color with a sandy and crumbly taste like good Scottish shortbread ought to be. Or, to decorate: press large crystals of Swedish pearl sugar into tops before baking; or after they have baked and cooled, ice with melted bittersweet chocolate, then dip in cocoa, powdered sugar, or sugar sprinkles.