Prepare pastry. Slice rhubarb (should yield 3 cups). Slice bananas (should yield 3 cups). Combine ingredients except butter and crust. Spread into pie crust. Dot with butter. Place crust on top. Bake at 230ºC for 15 minutes. Reduce oven temperature to 180ºC and bake for an additional 20 minutes or until browned.