Preheat oven to 425 degrees. Roll out your pastry and put it in your pan.
Fill with your rhubarb.
Mix together the sour cream, sugar and 1/3 cup flour and pour over top the rhubarb.
Cut together the 1/2 cup flour, butter and brown sugar and sprinkle over top the pie.
Bake on bottom shelf for 10 minutes at 425 and then reduce heat to 350 and bake for 40-50 minutes until rhubarb is cooked and the top is brown.