In a heavy medium saucepan stir together first 5 ingredients. Cook, stirring constantly over medium heat until thinkened and bubbly, keep warm.
For Meringue, place the egg whites and cream of tartat in a large clean mixing bowl. Beat with an electric mixer on medium speed until you get soft peaks. Slowly add sugar, one tablespoon at a time. Beating on high for about 4 minutes until stiff glossy peaks form.
Pour warm filling into baked pie chell. Spread meringue over filling. Bake in a 350 oven for 15 minutes. Remove and cool on wire rack for 1 hours. Chill 3-6 hours before serving. Cover for longer storage.