Stir the flour, salt, and baking powder together in a large bowl. Set aside.
Using an electric stand or hand mixer, mix the butter and powdered sugar in a large bowl on low speed until they are combined. Then increase to medium-high speed for 2 minutes, until light and fluffy. Scrape the sides.
Add the egg and beat for an additional minute. Mix in the lemon zest and 2 tablespoons lemon juice using medium speed.
Add the flour mixture and stir at low speed until the dough comes together and no flour is visible. Cover and refrigerate for at least 1 hour, or overnight
When ready to bake, preheat the oven to 350°F (177°C). Use a small cookie scoop or tablespoon to portion the dough into 1-inch balls. You can roll them in your hands if you want them to be uniform. Place the dough on a cookie sheet with 3 inches between each ball and gently press with your hand or a spatula to flatten.
Bake for 10-12 minutes until the edges are just beginning to brown. The middle of the cookie may still look wet. Cool for 5 minutes on the baking sheet and then transfer to a cooling rack to cool completely.
Once the cookies have cooled, whisk the confectioners’ sugar, 2 tablespoons of lemon juice, and butter in a small bowl. Spread or drizzle the cookies.
Notes
For larger cookies, use a 2 tablespoon scoop and bake for 12-15 minutes.Glaze: If you wish to frost the entire cookie then double the glaze ingredients so that you have enough.Storage: Store at room temperature or in the refrigerator for up to a week. The cookies can also be frozen for up to 6 months.