Preheat oven to slow (250°). Grease and flour 2 cookie sheets. Combine pistachios and chocolate in blender or food processor. Cover; whirl until very finely chopped. Reserve. Beat together egg whites and cream of tartar in small bowl until soft peaks form. Gradually beat in sugar, 1 tablespoon at a time, until mixture forms very stiff peaks. Fold in chocolate mixture and vanilla. Using a teaspoon, drop small mounds of meringue on prepared sheets, leaving 1 inch between. Bake in preheated slow oven (250°) for 30 minutes or until firm but not browned. Let stand several minutes on cookie sheets. Loosen meringues carefully with small knife; transfer to wire rack to cool completely. Store in tightly covered container in a dry place. Nutrient value Per Cookie: 28 calories, 0 gm. protein, 1 gm. fat, 5 gm. carbohydrate, 0 mg. sodium, 3 mg. cholesterol. cook 0