Food coloring, as needed
Kosher salt
1/2 teaspoon Cream of tartar
3 Large egg whites
1 pound Confectioners’ sugar
1 Large egg
2 teaspoons Vanilla extract
1 1/2 cups Confectioners sugar
1 cup Unsalted butter
1/2 teaspoon Kosher salt
1 teaspoon Cream of tartar
1 teaspoon Baking soda
2 1/2 cups All-purpose flour, more for rolling