Heat oven to 200°. Line 2 large baking sheets with parchment paper.Advertisement
Combine egg whites, cream of tartar and salt in bowl of a stand mixer. Whip on medium speed until frothy. Increase to medium-high and gradually add sugar, a few tablespoons at a time, until glossy and very fluffy, about 3 minutes. Beat in vanilla.
Place 1 1/3 cups meringue into each of 3 bowls (leave remaining meringue in mixer bowl). Tint each bowl of meringue a different shade with green food coloring.
Spoon 1 bowlful of meringue into a pastry bag fitted with a large star tip. Holding bag 1/2 inch above surface, pipe onto prepared baking sheets. Repeat with remaining bowls. Bake 2 hours. Cool completely on pans. Makes about 60 cookies.