Lemon extract, juice, and zest all provide amazing lemon flavors, but they are very different and provide different "types" of lemon flavor. I used all three in this recipe so you get the best of all words! Extract provides a "base" lemon flavor, exactly what you expect from a lemon cookie. Lemon juice provides a sharper, real lemon flavor that would set apart a basic cookie from a great cookie. Lemon zest provides a lasting real lemon flavor and a great chewy texture.