1. Preheat the oven to 325°F (170°C) with a rack set in the middle position.
2. In the mixing bowl of the stand mixer fitted with the flat beater attachment, beat butter and granulated sugar on medium-high (7–8) speed until light and fluffy, 2–3 minutes.
3. Reduce the mixer speed to low (1–2) and add 4 cups (500 grams) flour, ½ cup (63 grams) at a time, until well blended. Scrape down the bowl as needed.
4. Divide the dough in half. Dust a cutting board and rolling pin with flour. Roll each half to ¼-inch (0.6-centimeter) thickness. Cover with plastic wrap and refrigerate for  1 hour. Cut the chilled dough with a 2½-inch (6-centimeter) plain or fluted round cookie cutter.
5. Place the cookies on an ungreased cookie sheet. With a fork, prick each cookie in 3 rows, pressing all the way through the cookies.
6. Bake until the cookies are golden brown, 18–20 minutes. Let cool on the baking sheet for 10 minutes. Move the cookies to a wire rack and let cool completely.

Variations:

Scottish Shortbread

1. Follow step 1.
2. In step 2, substitute 1¼ cups (275 grams) firmly packed dark brown sugar for granulated sugar and add 2 teaspoons (8 milliliters) vanilla extract.
3. In step 3, substitute 4 cups (508 grams) bread flour for all-purpose flour and add ½ teaspoon (3 grams) salt.
4. Continue as directed.

Spicy Orange Ginger Shortbread

1. Follow step 1.
2. In step 2, add 1 tablespoon (6 grams) grated orange zest to the butter mixture.
3. In step 3, add 2 teaspoons (4 grams) Chinese five-spice powder with the flour. After blending in the flour mixture, use the pulse function to add ½ cup (65 grams) finely chopped crystallized ginger.
4. Continue as directed.

Pro Tip
In step 4, to avoid using additional flour, roll the dough between two sheets of parchment paper.