Coat each Dutch Oven with 1 TBL oil, cut plums in half and place one layer flat side down. Remove the rhubarb from Ziploc bag without getting liquid. Do not put the liquid in the DO (Dutch Oven), it will make it too watery. Layer rhubarb over the plums, one bag per DO. Next, layer the brown sugar, approx. 1/2 cup per DO. Next, layer the DRY white cake mix, one bag per DO. Drop dollops of butter on the white cake mix. Cover and bake on coals until brown and bubbly.
LEAVE SOME WITHOUT CAKE MIX TOPPING IF ANYONE GLUTEN FREE.
Serve with whipped cream.