1. In a large bowl, beat 1 cup of the sugar with the butter until light and fluffy. 2. Sift together the flour and cornstarch and gradually mix into the creamed butter. Gather the dough into a ball and flatten into a disk. Wrap in waxed paper and refrigerate for 1 hour. 3. Preheat oven to 225F. Trace a 12-inch circle on a large baking sheet. Pat out the chilled dough to fit the circle, taking care that the top is even and smooth. Score the top of the pastry into 8 equal wedges. Press decorative designs into the edges, if desired. 4. Bake the shortbread in the upper middle of the oven for 35 minutes; do not allow to color. Remove from the oven, sprinkle with the remaining 2 tablespoons sugar and let cool on the sheet. Break into wedges before serving.