Buttery Shortbread

Adjust oven rack to middle position and heat oven to 425 degrees. Line ungreased 9-inch round cake pan with parchment round; set aside.

In bowl of standing mixer fitted with paddle attachment, mix flours, all but 1 tablespoon sugar (reserve for sprinkling), and salt at low speed until combined, about 5 seconds. Cut butter into 1/2-inch cubes with 1/4 cup flour mixture on a sheet of parchment paper. Add butter and any remaining flour on parchment to bowl with dry ingredients. Mix on low speed until dough is pale yellow and resembles damp crumbs, about 4 minutes.

Remove bowl from mixer and toss mixture lightly with fingers to fluff and loosen; rub any remaining butter bits into flour mixture with fingertips. Follow illustrations 1 through 5 to form and unmold shortbread. Place shortbread in oven; immediately reduce temperature to 300 degrees. Bake 20 minutes; remove baking sheet from oven and follow illustration 6 to score and pierce shortbread. Return shortbread to oven and continue to bake until pale golden, about 40 minutes longer. Slide parchment with shortbread onto cutting board, remove cutter from center, sprinkle shortbread evenly with reserved 1 tablespoon sugar, and cut at scored marks into wedges. Slide parchment with shortbread onto wire rack and cool to room temperature, at least 3 hours. (Can be wrapped well and stored at room temperature up to 7 days.)