Sour Cream Apple Pie

"It's a great pie, and everyone at the holiday party I took it to was thrilled." -laebrown
Preheat the oven to 400°F. Cool the pie dish while the filling is being prepared.Whisk together sour cream, egg, lemon juice and vanilla. Peel the apples, cut them into quarters and core, then cut them into thin slices; add the slices to the sour cream mixture and mix well. Spoon the apple mixture into the pie dish. Bake the pie for 30 minutes, reduce the oven temperature to 350 ° F and bake for 20 minutes.Melt the butter. Combine the flour, brown sugar, granulated sugar, walnuts, cinnamon, and salt, followed by the melted butter. Sprinkle the mixture over the baked pie and bake for another 20 minutes, or until the apples are tender. Allow to cool completely, then refrigerate for at least 1 hour before serving.