Stiffened, sweetened egg whites can be used for many purposes -- for simple cookies such as these kisses, for vacherin and dacquoise, and as the base of a wedding cake frosting. This recipe is from "Entertaining," by Martha Stewart.
Preheat oven to 225 degrees. Line 2 large baking sheets with aluminum foil.
Beat the egg whites until foamy. Add the salt, cream of tartar, and vanilla and continue beating. Add the sugar 1 teaspoon at a time, beating about 30 seconds between additions. When all the sugar has been added, beat an additional 6 minutes. Egg whites should be very stiff, glossy, and extremely smooth, but not dry.
Spoon the mixture into a large pastry bag fitted with a 1/2-inch star tip and pipe out "kisses," leaving 1-inch spaces. Reduce oven temperature to 200 degrees and bake for 1 1/2 to 2 hours, until the meringues are dry to the touch and can be lifted from the foil. Cool completely before storing in a cool dry place.