Combine first six ingredients with a fork until crumbly. Press into a greased 9x13" baking pan. Combine filling ingredients. Mix well. Pour over crust. Bake at 350 F. for 50-60 minutes. In a mixing bowl, beat egg whites unitl stiff. Gradually add sugar and vanilla, beating well. Spred over hot filling. Return to the oven for 10-15 minutes, until lightly browned.