To make Scottish shortbread, cream 2 cups of softened butter with 1 2/3 cups sugar. Mix 4 cups all-purpose flour with 1 1/3 cups cornstarch in a separate bowl, then slowly blend into the butter mixture. Roll to 1-inch thickness and bake 30 minutes at 350 F.
Sprinkle the shortbread with additional sugar while warm, if desired. When cool, either cut into pieces with a knife, or leave whole and break into pieces when serving. To ensure a tender texture, thoroughly cream the butter and sugar until light and fluffy, and avoid over-mixing the dough once the flour is incorporated.
Another classic recipe calls for 1 1/4 cups all-purpose flour, 1/4 cup rice flour, 1/4 cup granulated sugar and 1 1/4 sticks of pure butter cut into pieces. Sift together the flours and sugar, then knead in the butter. Roll out on a floured surface to a thickness of 1/3-inch and cut into finger shapes with a knife, or cut with a round cutter. Bake on an ungreased cookie sheet at 375 F until lightly tan on edges, but remove from the oven before the cookies brown. A variation on this recipe calls for 1 teaspoon vanilla, kneaded into the dough along with the butter.