Preheat 45 charcoal briquettes until white and glowing. Lightly grease the bottom of a cast iron camp dutch oven with cooking spray (see Notes).

In a medium bowl combine the cake mix and lemon lime soda. You want a batter that is thick, but moist (it does not have to be precise, I've had varying consistencies from stiffer batters to thinner cake-like batters).

Place fruit in the cast iron dutch oven and spoon batter over top. Top with bits of butter. Sprinkle with the sugar, if using. Cover the dutch oven with its lid.

Place 15 hot charcoal briquettes together and set dutch oven over them. Using tongs, place the remaining 30 briquettes on the dutch oven lid. (This exact number and placement is required to achieve 350 degrees inside the dutch oven.) After about 10 minutes, rotate the dutch oven over the coals clockwise and the lid over the dutch oven counter clockwise to promote even cooking. Check after 20 minutes, cobbler is done with the topping is golden brown and the fruit juices are bubbling.

Remove dutch oven from coals. Serve the cobbler with whipped cream.