If desired, substitute ⅓ cup (40g) rice flour or cornstarch for an equal amount of the all-purpose flour, which produces an especially crumbly and tender shortbread.
Preheat the oven to 300°F. Have ready an ungreased 8-inch square baking pan or a rectangular shortbread mold.
Beat in a large bowl until smooth:
Stir in:
Lightly knead until blended. Press the dough evenly into the baking pan or shortbread mold. If baking in a pan, pierce the dough deeply with a fork all over in a decorative pattern. If desired, sprinkle with:
Bake until the shortbread is lightly browned and darker at the edges, 45 to 50 minutes. Cut into bars while still warm, then let cool in the pan or mold.