Place cookie sheet on oven rack. Heat oven to 400°. In 1-quart saucepan, cook 1/4 cup butter over medium heat until melted and lightly browned, stirring constantly. Cool completely, about 15 minutes. In large bowl, beat 1/2 cup granulated sugar and egg with wire whisk until light and fluffy. Beat in 2 tablespoons all-purpose flour and 1 teaspoon vanilla. Beat in cooled butter. Gently stir in apples. Pour into frozen pie crust. In medium bowl, stir together all streusel ingredients except butter. With pastry blender or fork, cut in 1/4 cup butter until mixture looks like coarse crumbs. Sprinkle over apples. Place pie on cookie sheet in oven. Bake 20 minutes. Reduce oven temperature to 350°, and cover edge of crust with strips of foil to prevent excessive browning. Bake 40 to 50 minutes longer or until apples are tender and crust is golden brown. Cool 2 hours. In small bowl, beat whipping cream until soft peaks form. Add remaining topping ingredients; beat until stiff peaks form. Pipe or spoon onto pie.