Mix the first four ingredients together. (Rhubarb, brown sugar, flour and melted butter) Pour in a greased 7 x 11 or 9 x 9 baking dish.
Mix the remaining ingredients. Pour over the rhubarb mixture. Lay a piece of foil over the top.
Bake 350 degrees at 30-40 minutes.
Serve with ice cream or whipped cream