1. Beat the egg whites until light and frothy. Add the cream of tartar and continue beating until the whites are stiff enough to hold a peak.
2. Gradually beat in the sugar and beat until the meringue is stiff and glossy.
3. Pile the meringue lightly on cooled pie filling, spreading it until it touches the edges of the pastry to prevent the meringue shrinking.
4. Bake in a preheated hot oven (425° F.) until the top is brown, five to six minutes.