1 ¼ cups flour
½ teaspoon baking powder
¼ teaspoon salt
4 Tablespoons butter (softened)
¾ cup sugar
1 large egg white
1 teaspoon finely grated lemon zest
2 Tablespoons lemon juice
2 cookie sheets lined with parchment or foil
Set racks in the upper and lower third of the oven and preheat to 350 degrees. Stir the flour, baking powder and salt together and set aside. Beat the butter and sugar together by machine with the paddle attachment on medium speed for about a minute or until well mixed. Beat in the egg white and lemon zest. Change the speed to low and beat in half the flour mixture, then the lemon juice. Beat in the rest of the flour mixture. Use a large rubber spatula to give the batter a final mixing. Drop the batter with a teaspoon or small ice cream scoop about an inch apart in all directions onto the prepared pans. Bake the cookies for 8-10 minutes, or until they are light golden on the bottom but still very pale on the top. Change the position of the pans, from top to bottom and back to front, about halfway through the baking time (they will firm up when cooling). Slide the papers from the pans to the racks to cook the cookies.
Optional icing: Keep mixing together lemon juice and confectioner’s sugar until you achieve the consistency you want. Spread the icing over cookies while they’re still a little warm so that it melts over the sides a bit.
Storage: Keep the cookies between sheets of wax paper in a tin or plastic container with a tight-fitting cover.