Rhubarb Butter Crunch

This is one my friend's Tracy favorite rhubarb dessert.  The topping is SO good.

3 cups rhubarb
1 cup sugar
3 tsp flour
1 1/2 cup flour
1 cup brown sugar
1 cup oatmeal
1/2 cup butter

Combine rhubarb, sugar and 3 tsp flour. Place in greased 9x9 pan.  Combine brown sugar, 1 1/2 flour, oatmeal, and butter.  Sprinkle over top.  Bake at 350 for 40 minutes.