1Preheat an oven to 350 degrees F (175 degrees C). Roll out the pastry and transfer it to a 9-inch pie plate. Trim any extra dough and crimp the edge.
2Combine 1/2 cup sugar, sour cream, 1/4 cup flour, egg, vanilla, and salt in a bowl until blended. Fold in the pears. Pour the mixture into the pie plate and bake the pie for 15 minutes.
3While the pie is baking, prepare the topping: mix the 2/3 cup flour, 1/3 cup sugar, melted butter, and rolled oats together in a bowl.
4Remove the pie from the oven and sprinkle with the crumble topping. Return the pie to the oven and bake until the filling is set and the crust is brown, about 20 minutes more. Allow to cool and set before serving.