Melt 4 tablespoons butter in 10 cast iron skillet, over med heat. Add brown sugar and stir. Increase heat to med-high and cook until bubbly, about 2 min. Arrange pineapple in skillet and continue to cook 2 mins, till mixture turns amber. Remove from heat. It will continue to cook even with heat is off. Arrange pecans cherries among pineapple. Set aside to cool slightly.

Preheat the oven to 375 degrees F. Stir together the flours, baking powder, baking soda, and salt in a medium mixing bowl.

Cream 1/2 cup butter and sugar until fluffy. Add eggs, 1 at a time, mixing till incorporated. Add flour mixture and buttermilk alternately in 3 batches, mixing on low until just combined. Stir in vanilla and rum.

Spoon batter over pineapple slices in the skillet. Bake in the middle of the oven until golden brown and a tester comes out clean, 35 to 40 mins.

Cool the cake in the skillet on a wire rack for 4 minutes only. Run a thin knife around the edge of the cake and, wearing oven mitts and working quickly, invert the cake onto a cake plate, keeping plate and skillet firmly pressed together. Carefully lift the skillet off cake and replace any fruit stuck to the bottom of the skillet, if necessary.

Serve cake warm or at room temperature.

In 12 dutch oven: For 375: 9 coals on bottom 18 coals on top