Split grapes carefully and remove seeds. Mash lightly with water. In a separate bowl, combine the 1 cup sugar, butter, cornstarch, and egg yolks; mix well. Fold in grape mixture. Pour into an unbaked pie shell. Bake at 350-degrees for 45 minutes. Remove from oven.

Make a stiff meringue with the 3 egg whites and 2-3 tablespoons sugar. Spread on top of baked pie. Return to oven to bake for another 20 minutes or until lightly browned.