Mouth-puckeringly tart AND satisfyingly sweet, these crunchy, sugar-coated cookies are bound to quickly become a family favorite.

Cookies
3/4 cup (1 1/2 sticks) unsalted butter
3/4 cup granulated sugar
1/2 teaspoon salt
1 teaspoon baking powder
2 tablespoons Key Lime Juice
1/8 teaspoon lime oil
1/8 teaspoon sour salt (citric acid)* OR 1/2 teaspoon Tart & Sour Flavor
1 large egg 2 1/2 cups King Arthur Unbleached All-Purpose Flour

Coating
1/8 teaspoon sour salt (citric acid*)
1 cup glazing sugar or confectioners' sugar
2 tablespoons white edible glitter (optional)

*Sour salt (citric acid) is what gives the cookies their sour bite—if you want less tang, use just a pinch.

In a medium-sized bowl, beat together the butter, sugar, salt, and baking powder till well blended. Beat in the lime juice, lime oil, sour salt (citric acid), and the egg. Blend in the flour thoroughly.

Roll the dough into 1" balls, and place them on lightly greased or parchment-lined baking sheets. Bake the cookies in the top third of a preheated 350°F oven for 14 to 16 minutes, until the cookies are browned on the bottom. Remove them from the oven, and cool on the pan for about 10 minutes before transferring to a rack.

Mix together the sugar coating ingredients in a pan or bag. Gently shake and roll the still slightly warm cookies in the sugar till coated. Allow the cookies to cool completely, then repeat, coating again with the sugar. (If you're freezing the cookies, you may choose to recoat the cookies in sugar once they've been removed from the freezer, before serving.) Yield: 3 dozen cookies.