Combine rhubarb, 1 tablespoon flour and white sugar. Mix well and place in pie shell.
Melt the butter or margarine and mix with 1/2 cup brown sugar, crushed corn flakes and 1/2 cup flour. Mix in a bowl and pat down on top of pie. Bake in oven at 350 degrees F (175 degrees C) for about 40 minutes. Turn off oven and leave the pie in the oven for another hour. Serve warm.