Beat egg whites with cream of tartar until foamy in a small deep bowl. Gradually beat in sugar to make a stiff meringue. Fold in M&M's. Grease and flour a large cookie sheet. Drop meringue mixture by teaspoonsful onto cookie sheet. Garnish each with an M'M. Bake in slow oven (250) for 30 min. or until cookies are firm to touch, but still white. Cool cookies on cookie sheet on wire rack. Remove from sheet with spatula. Store in container with tight cover.