Preheat the oven to 350 degrees and lightly coat a baking sheet with nonstick spray.
Sift the powdered sugar and cornstarch into a medium bowl or the stand mixer along with the softened butter. Mix until the butter begins to break up.
Add the flour and mix together until a dough-like consistency forms.
Roll out the dough to a ½ inch thickness. Mine measured 11 inches by 6 inches. Cut into fingers or circles. Dock with a fork if you like for that trademark shortbread marking.
Transfer the cut cookies to the prepared baking pan. Bake for 10 to 15 minutes or until golden in color.
Remove from the oven, transfer to a cooling rack and sprinkle with granulated sugar.
Notes
European-style butters like Plugra, Kerrygold, or Président have a higher butterfat content than standard American butter. This gives the cookies a wonderfully rich flavor but can also make the dough softer and more prone to spreading. To help, chill the dough well before rolling and baking, or add 1–2 tablespoons of flour. You can also reduce the butter slightly (14 tablespoon instead of 16) for a sturdier dough — without losing that buttery flavor.
Chill the dough: Refrigerate at least 30 minutes before rolling, and again after cutting shapes if the dough softens. Cold dough helps cookies hold their shape.
Baking tip: Shortbread should be pale, not golden brown. Remove from the oven as soon as the edges begin to turn lightly golden.
Cutting shapes: Reroll scraps gently to keep cookies tender. For the neatest edges, use sharp cutters and press straight down without twisting.
Storage: Store cooled cookies in a tin or airtight container at room temperature for up to 2 weeks. Their flavor actually deepens after a day or two. They also freeze well for up to 3 months.
Perfect for gifting: These cookies hold up beautifully when packed in tins or gift boxes and are a festive choice for Christmas cookie exchanges or holiday giving.