- 4 cups chopped rhubarb
- 2 cups sliced strawberries
- 1 (3 ounce) package strawberry-flavored gelatin mix (such as Jell-O®)
- 1/4 cup white sugar, or more to taste (optional)
- 1 (15.25 ounce) package yellow cake mix
- 1 cup warm water
- 1/4 cup butter
- Preheat oven to 350 degrees F (175 degrees C). Grease a 9×13-inch baking pan.
- Place rhubarb and strawberries in baking pan. Evenly spread strawberry-flavored gelatin mix over fruit, then repeat with cake mix. Pour water over cake mix layer; do not stir. Dot the top of the cake with butter.
- Bake in the preheated oven until cake is bubbly, about 20 minutes.