Heat oven to 350 degree F. Coat an 11 x 7 x 2-inch baking dish with nonstick cooking spray.Advertisement
Place rhubarb in the prepared baking dish and sprinkle with granulated sugar and then with gelatin. Sprinkle the cake mix over the gelatin and then drizzle with 3/4 cup water. Stir in the melted butter.
Bake at 350 degree F for 50 minutes. Remove from oven and cool on a wire rack for 10 to 15 minutes.
Serve warm or at room temperature. Dust with confectioners sugar and serve with whipped topping, if desired.