Combine pumpkin, milk, 1/2 cup brown sugar, eggs, flour, spices, and salt; beat 1 minute or until smooth at medium speed of an electric mixer. Pour into pastry shell; bake at 350° for 45 minutes.
Combine butter, 1 cup brown sugar, and pecans; mix well. Sprinkle pecan mixture evenly over top of pie. Reduce heat to 325°, and bake 25 minutes. Cool before serving.