Combine the brown sugar, water and vinegar in a saucepan. Bring to a boil. Add apples and cook until tender. Remove apples from syrup and set aside. Cream together butter and flour. Stir into hot syrup and cook until thickened and smooth, stirring constantly. Add salt and fold in apples. Cool. Turn into baked pie shell. Add sugar and vanilla and beat until just combined. Spread meringue over pie filling.
Meringue: 2 egg whites, 4 T. sugar, 1 tsp. vanilla
Bake at 350 degrees for 9 - 10 minutes until meringue is lightly browned.