Line a deep dish pie plate with pie crust and form a decorative edge. In large bowl beat eggs lightly and stir in sour cream, sugar, flour, vanilla, and salt until smooth. Toss in apples and stir to coat. Spoon into pie shell. Bake 10 minutes. Lower oven to 350 degrees F. Bake for 35 minutes. Combine butter with rest of ingredients with fork or pastry blender. Sprinkle topping over pie and bake for 15 minutes. Cool to room temperature and chill. Serve chilled.