Peel and core the pineapple. Cut it into 1/2-in-thick planks. Set aside.
In a skillet over medium heat, combine the unsalted butter, brown sugar, and dark rum.
Cook the mixture until the butter is melted, stirring continuously, for about 1 minute.
Arrange the pineapple slices in a single layer in the skillet.
Spoon the liquid over the pineapple to coat them evenly.
Sauté the pineapple until it turns a golden-brown color, turning once to ensure even caramelization.
Once the pineapple is caramelized, carefully remove it from the pan and place it on a sheet pan.
Using a heat-proof rubber spatula, scrape the remaining caramel from the bottom of the pan onto the pineapple.
Transfer the caramel-coated pineapple to a baking dish and place it under the broiler for about 8 minutes or until the sugar starts to burn. Keep a close eye on it to prevent burning; the goal is to achieve a nice, caramelized crust.
Allow the planks to cool and dice them into 1/2-in chunks. Reserve.
