1 1/2 cups (3/4 lb.) butter at room temperature (no substitutes)
2/3 cup sugar
2 Tbsp. very finely chopped lavender florets (fresh or dried)
1 Tbsp. chopped fresh mint
2 1/3 cups flour
1/2 cup cornstarch
1/4 tsp. salt
Preheat oven to 325°F. Cover bottoms of two baking sheets with parchment or brown paper. In a large bowl, cream together butter, sugar, lavender, and mint with an electric mixer. Mix until light and fluffy, about three minutes. Add flour, cornstarch, and salt and beat until incorporated. Divide dough in half. Flatten into squares and wrap in plastic. Chill until firm. On a floured board, roll or pat out each square to a thickness of 1/2 inch. Cut the dough into 1 1/2 -inch squares or rounds.
Transfer to baking sheets, spacing cookies about one inch apart. Prick each cookie several times with a fork. Bake 20 to 25 minutes until pale golden (do not brown). Cool slightly, transferring to a rack. Sprinkle with lavender powdered sugar.* Makes about 4 dozen.
*Put four or five sprigs of lavender flowers in a sealed jar with powdered sugar for a day before using the sugar.