Prep. Preheat your oven to 350°F (175°C). Then, line a baking sheet with parchment paper to prevent sticking.
Mix dry ingredients. Whisk together the all-purpose flour, baking powder, and salt in a medium mixing bowl. Set this aside.
Cream butter and sugar. Using an electric mixer, cream the unsalted butter and sugar in a large bowl until the mixture is light and fluffy, approximately 3-4 minutes. Then, beat in the egg, followed by the lemon zest and freshly squeezed lemon juice.
Combine. Slowly add the dry ingredients to the wet mixture. Mix until just combined. The dough may appear crumbly at first, but should hold together when pressed.
Make topping. Combine ½ cup of sugar in a small bowl with 1 tablespoon of lemon zest. Stir until evenly mixed.
Form the cookie dough balls. Use a cookie scoop or spoon to shape tablespoon-sized portions of dough. Roll each dough ball in the lemon sugar mixture, ensuring an even coating. Place the balls on the prepared baking sheet, spacing them about 2 inches apart.
Flatten the cookies. Using the bottom of a glass, gently press each dough ball to flatten slightly.
Bake. Bake the cookies for 10-12 minutes or until the edges are slightly golden. Avoid overbaking to keep the cookies soft. Allow them to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
Cool and serve. Let the cookies cool completely before serving to settle the flavors and perfect the texture. Enjoy with a cup of tea or your favorite warm drink!