Preheat the oven to 350°F. Grease (or line with parchment) two baking sheets., In a small bowl, stir together the flour, cornstarch, baking powder, salt, Lemon Crumbles, and Lemon Juice Powder. Set aside., In a separate bowl, beat together the butter, sugars, and lemon zest until creamy., Add the vanilla and lemon extracts and egg, beating until well incorporated., Add the flour mixture and stir just until combined., Drop the cookies by the tablespoonful onto the prepared baking sheets, spacing them about 2" apart (a tablespoon cookie scoop works well here), and flattening the balls slightly with a fork or the bottom of a glass dipped in granulated sugar., Bake the lemon cookies for 11 to 13 minutes, until golden., Remove the lemon cookies from the oven and cool for 2 minutes on the baking sheets before transferring them to a rack to cool completely.