Preheat and prepare the cooking sheets. Preheat the oven to 375° Fahrenheit. Line two baking sheets with parchment paper or silicone baking mats (or gently coat with nonstick cooking spray).
Whisk together the dry ingredients. In a larger basin, combine the flour, baking powder, baking soda, and salt. Set aside.3 cups (360 g) all-purpose flour and 1 teaspoon baking powder.1/2 teaspoon baking soda.½ teaspoon salt.
Cream together butter and sugar. Cream the butter and sugar in a large basin with an electric mixer for about 2 to 3 minutes, or until light and fluffy.1 cup (2 sticks, 226 g) unsalted butter and 1 ¼ cups (250 g) granulated white sugar.
Add the remaining wet ingredients. Add the egg and beat until combined. Combine vanilla, lemon juice, and lemon zest. Beat to blend. Scrape down the bowl as needed. One huge egg.1 teaspoon of vanilla extract.2 teaspoons of lemon juice.1 tablespoon of lemon zest.
Add the dry ingredients. Add the flour mixture and mix on low to medium speed until no flour streaks remain.
Combine the dry ingredients. Add the flour mixture and mix on low to medium speed until there are no flour streaks left.
Bake and cool the cookies. Bake for 10–12 minutes. The edges will look finished, but the middle will still appear slightly soft. Remove from the oven and allow cool on the baking sheets for 5 minutes before transferring to a wire rack to finish cooling.
Make icing. In a small mixing bowl, combine icing ingredients. Use an offset spatula to spread icing over the top of each cookie. Adjust consistency if needed. 2 cups (228 g) of confectioners sugar. 3-4 teaspoons of lemon juice. 2 tsp lemon zest, ½ tsp vanilla essence