Prepare Big Green Egg for indirect cooking at 350°F
Place ½ cup (1 stick) butter in a 12 inch Cast Iron Skillet or Aluminum Foil half pan lined with parchment paper and place in the Egg about 3-5 minutes or until butter has melted.
When butter has melted, remove pan. Stir in rum, then pineapple, stir to combine.
Spoon the dry cake mix from the box evenly over pineapple. Sprinkle coconut on top.
Cut remaining ½ cup (1 stick) of butter into small cubes and place cubes of butter over cake mix and coconut.
Bake dump cake for 45-60 minutes until cooked through and coconut is toasted. Check cake every now and then to make sure coconut does not burn. if coconut starts to get too toasted, cover with aluminum foil.
Dessert will firm up more as it cools. Serve warm or cold. Refrigerate leftovers or until ready to serve. Top with ice cream if desired. Enjoy!