This is an old recipe handed down to me by my grandmother. It's really one of the best pies I've ever tasted.
Preheat oven to 400 degrees F (200 degrees C).
Whisk together the 3/4 cup sugar, the 2 tablespoons flour, and salt. Beat in the sour cream, egg, and vanilla. Stir in the sliced peaches. Pour the mixture into the pie crust.
Bake in the preheated oven for 12 minutes. Reduce the oven temperature to 350 degrees F (175 degrees C), and continue baking until the filling is set, about 30 minutes. Remove from oven.
Raise oven temperature to 400 degrees F (200 degrees C).
Whisk together the 1/3 cup flour, 1/3 cup sugar, and cinnamon in a small bowl. Mix in the butter with a fork until mixture resembles coarse crumbs. Sprinkle the crumb topping evenly over the pie.
Return the pie to the preheated oven and bake until topping is golden, about 10 minutes. Let pie cool slightly before slicing.