Upside Down Rhubarb Cake

Preheat oven to 350 degrees F (175 degrees C).

Grease a 9x13-inch baking pan.

Mix rhubarb, sugar, strawberry gelatin mix, and tapioca in a bowl.

Spread the rhubarb mixture into the bottom of the prepared baking pan.

Beat white cake mix, water, vegetable oil, and eggs in a large mixing bowl until moistened; beat with an electric mixer on medium speed for 2 minutes.

Pour the cake batter over the rhubarb mixture.

Bake in the preheated oven until a toothpick inserted into the middle of the cake layer comes out clean, about 35 minutes.

Let cake stand for 5 to 10 minutes before inverting on a plate.