Preheat oven to 350 degrees Fahrenheit. Place rhubarb and sliced strawberries in pan, sprinkle sugar over it, then evenly sprinkle the gelatin over top.
Thoroughly mix your dry cake ingredients together and sprinkle evenly over rhubarb. Pour your 1 cup water over all of this and dot with 3 tablespoons chopped butter. Don’t stir!
Bake at 350 for 1 hour. Serve this warm by itself, or add a dollop of whipped cream or vanilla ice cream. My husband says the rhubarb counts as a vegetable and eats it for breakfast, too.