Preheat oven to 350 degrees. Mix yellow cake as directed on box. Pour into a greased 9 by 13 inch baking pan. Sprinkle rhubarb over top of cake. Do not mix in. Sprinkle sugar over rhubarb. Then slowly pour cream over top of all.
Bake at 350 degrees for 40-45 minutes. Cool 15-20 minutes before cutting. Serve with whipped cream.
NOTE: If you like you can add 1 teaspoon cinnamon to the sugar before sprinkling it on cake.