Combine egg whites (at room temperature), vanilla, and cream of tartar in a medium glass or metal mixing bowl; beat until foamy. Gradually add sugar, 1 tablespoon at a time, beating until stiff peaks form and sugar dissolves.
Spread meringue over hot pie filling, carefully sealing to edge of pastry to prevent shrinkage. Bake as directed in each pie recipe.
Note: A copper bowl is excellent for beating egg whites. The chemical reaction which occurs between the copper and egg whites helps to stabilize the mixture. Cream of tartar should be omitted when beating egg whites in a copper bowl.