Ingredients for 16 servings:
1. 1 1/4 cups cold unsalted butter
2. 1/4 cup powdered sugar
3. 1/4 cup granulated sugar
4. 2 1/2 cups all-purpose flour

Directions:
1. Set oven rack to middle position.
2. Preheat oven to 275°F.
3. Have two ungreased 8-inch cake pans ready.
4. Food Processor Method.
5. Cut the butter into 1-inch cubes, wrap it, and refrigerate.
6. Process the sugars for 1 minute or so, until the sugar is very fine.
7. Add the butter and pulse until the sugar disappears.
8. Add the flour and pulse until there are a lot of moist, crumbly little pieces and no dry flour particles remain.
9. Dump the mixture into a plastic bag and press it together.
10. Remove the dough from the plastic bag and knead it lightly until it holds together.
11. Electric Mixer or by Hand.
12. Use superfine granulated sugar for the best texture and be sure to soften the butter.
13. In a medium bowl, whisk together the sugars.
14. In a large bowl, cream the butter with the sugars until light and fluffy.
15. With your fingers or with the electric mixer, mix in the flour until the mixture holds together.
16. If using the mixer, add the flour in 2 parts.
17. For Both Methods.
18. Divide the dough into 2 equal parts.
19. Pat each half into an ungreased 8-inch round cake pan.
20. Use the tines of a fork to press 3/4-inch lines radiating like rays of sun all around the perimeter of the dough.
21. Prick the rest of the dough all over with the tines of the fork.
22. (this keeps the shortbread even and creates the traditional design).
23. Bake for 60-70 minutes or until pale golden (do not brown).
24. For even baking, rotate the pans from top to bottom and front to back halfway through the baking period.
25. Cool in the pans, on a wire rack, for 10 minutes.
26. Invert the shortbread onto flat cookie sheet and slide it onto a cutting board.
27. While still warm, use a long sharp knife to cut each 8-inch round of shortbread into 8 pie-shaped wedges.
28. Transfer the wedges to wire racks to cool completely.