For 9 inch pies:

3 egg whites
1/4 tsp. cream of tartar
1 tsp. vanilla
1/4 tsp. salt
6 tbsp. sugar

Have egg whites at room temperature for greatest volume. Place in bowl with cream of tartar, salt, and vanilla. Beat until mixture is frothy. Add sugar, a little at a time, making sure the sugar dissolves each time. Continue to beat until stiff peaks form. Arrange on top of filled pie, spreading it so that it touches inner edge of crust all the way around (prevents shrinkage).

Bake at 350°F for 15 minutes. Cool away from drafts. Lemon juice (1 teaspoon) may be substituted for the cream of tartar. In this case, omit vanilla.