The recipe is adapted from Baking Illustrated, by way of When Harry Met Salad. If you don't have lavender, try making these with an herbes de Provence mix that has lavender in it. Makes 4 dozen cookies.
3/4 cup granulated sugar
2 Tbsp grated lemon zest + 2 Tbsp juice, from 1-2 lemons
2 tsp dried lavender
1-3/4 cup all-purpose unbleached flour
1/4 tsp baking powder
1/4 tsp salt
12 Tbsp (1-1/2 sticks) cold unsalted butter, cut into 1/2-inch cubes
1 egg yolk
1/2 tsp pure vanilla extract
In a food processor, pulse the sugar, lemon zest and lavender until the sugar looks damp and the ingredients are fully incorporated, about 30 seconds.
In a bowl, whisk together the flour, baking powder and salt, and add this to the sugar mixture. Pulse 10 times to combine. Scatter the butter pieces over the flour, and pulse until the mixture resembles fine cornmeal, about 15 one-second pulses.
In a measuring cup, beat together the lemon juice, egg yolk and vanilla. With the machine running, add the juice mixture in a slow stream and continue processing until the dough forms a ball, 10-15 seconds.
Turn the dough onto a clean work surface, and gently gather into a ball. Working quickly, roll the dough into a cylinder 12 inches long and 1-1/2 inches in diameter. Wrap tightly in plastic wrap, twisting the ends together to seal (this helps the dough hold its shape). Chill the dough until firm and cold, 45 minutes in the freezer.
While the dough is chilling, preheat the oven to 375°F. Line two baking sheets with silicone baking liners (Silpats) or parchment paper.
Remove the dough log from the freezer, and unwrap it. With a very sharp knife, slice the dough into 3/8-inch thick rounds, and place the rounds on the baking sheets, spacing them one inch apart.
Bake until the centers of the cookies just begin to color and the edges are golden brown, about 12-14 minutes, rotating the baking sheets halfway through the baking time. Cool the cookies on the pans for 5-10 minutes, then transfer to a wire rack to cool completely.