Position a rack in the center of your oven. Preheat your oven to 350℉ (177°C) and line your cookie sheets with parchment paper.
In a large mixing bowl with an electric mixer (you can use a hand mixer or a stand mixer with paddle attachment) cream together the softened butter and sugar, until light and fluffy, about 2 to 3 minutes.
Beat in the lemon extract, vanilla extract, lemon juice, and zest until combined.
With mixer on low speed, beat in the flour, baking powder, and cornstarch and mix just until the cookie dough forms. Stop mixing once the last of the flour has been incorporated. Do not overmix.
Use a small cookie scoop (2 tablespoons), scoop the cookie dough, roll into a ball in your hands and then roll each cookie dough ball in the powdered sugar in a small bowl. Then place onto your cookie sheet, spaced about 1-2 inches apart.
Bake for 10-12 minutes, or until the edges are set and the bottoms of the cookies are slightly golden.
Allow to cool slightly and sift more powdered sugar on top of the cookies before enjoying!