Lavender Shortbread Cookies

8 oz. (2 sticks) unsalted butter, chilled
¼ cup lavender sugar
1/4 cup sugar
2 cups all-purpose flour (spoon and level; 9 ounces)

Fifteen minutes before you begin the dough, remove the butter from the refrigerator. Place the lavender sugar in a clean spice mill and grind until fine. If you don’t have a spice mill, grind the lavender in a blender or small food processor.

Mixing the dough: Transfer the lavender sugar to the bowl of a heavy-duty electric mixer fitted with a paddle and add the remaining 1/4 cup sugar if you used a spice mill and the butter. Beat on low speed until the mixture is s smooth and there are no detectable lumps of butter when you roll a teaspoon of it between your fingers; do not beat it until it is fluffy. Add all the flour at once and continue to mix on low speed just until it forms a cohesive dough.

Rolling and cutting: Turn the dough out onto a lightly floured surface, press it firmly into a smooth rectangular block with no cracks, and dust it lightly with more flour. Using a rolling pin, roll it into a 12 x 9-inch rectangle, 1/4 inch thick, rotating the dough a quarter turn each time you roll to make sure it is not sticking to the work surface. You an also roll the dough out between sheets of plastic wrap or parchment paper. Using a straight edge and a pastry wheel or chef’s knife, cut the dough into 3 x 1-1/2 inch bars, or cut out other shapes with cookie cutters. Using a spatula, transfer the cookies to a baking sheet lined with parchment paper, leaving 1/2-inch space between them. Refrigerate the cookies for at least 30 minutes before baking to allow the dough to rest.

Preheat the oven to 300 degrees Fahrenheit. Bake the cookies until they are colored lightly like sand, not browned, 22 to 25 minutes. Lift one with a small spatula to check the color of the underside; it should be just a shade darker on the top. Let the cookies cool completely on the pan (they are soft while they are hot). Stack the cooled cookies in an airtight container and store at room temperature for up to a week.

Mixing variation: If you don’t have a heavy-duty electric mixer, you can mix the dough in a large mixing bowl with a wooden spoon, but you’ll need to start with butter that is at room temperature. Mix the butter with the lavender sugar until completely smooth, and then stir in the flour. Wrap the dough in plastic wrap and refrigerate for about 1 hour before rolling.Herb substitutions:In place of the lavender sugar, add 4 teaspoons finely chopped fresh rosemary, thyme or lemon thyme plus ¼ cup sugar to the butter and sugar.