Prepare batter for 2 layer size yellow cake mix according to package directions. Put into 9"x13" oblong pan. Cover batter with 4 cups chopped rhubarb. Sprinkle rhubarb with 1 cup granulated sugar. Pour 1 pint whipping cream over ingredients in pan. Bake at 350 degrees for 50 to 60 minutes. Cream and rhubarb sink to bottom forming a custard layer. Store any left overs in refrigerator.