Preheat the oven to 350 degrees. Grease and lightly flour a 9 x 13 inch cake pan.

Place the rhubarb in a bowl and sprinkle sugar over top. Allow to sit while you prepare the other ingredients.

Prepare the cake mix according to package instructions then pour the batter into the prepared pan. Toss together the rhubarb and sugar then sprinkle evenly on top. There will likely be some extra sugar liquid at the bottom. Make sure you get that part too.

Slowly pour the cream evenly over the entire top of th ecake.

Place the cake in the oven and bake for 50 minutes to 1 hour, or until top is set and a toothpick comes out clean (the bottom third of the cake will still be wet so don't base the toothpick test on that portion). Serve the cake warm with a spoon (the custard will be delicious but runny), or chill for a few hours or overnight to allow the custard to set up and slice neatly. We love the cake both warm and cold!