Combine the rum and brown sugar in a dish and whisk together until combined.

Arrange the pineapple slices along the bottom of a 9x13" baking dish and pour the rum and brown sugar mixture over the pineapple. Let it soak for 2-6 hours, flipping the pineapple half way through to allow the rum to soak into both sides.

Remove the pineapple from the rum mixture and pour the rum mixture into a small saucepan. To make the salted caramel sauce, bring the mixture to a boil over medium high heat and cook until it is slightly thickened and reduced by about 2/3. Remove from the heat and add the cold butter and sea salt. Swirl the saucepan to gently incorporate the butter and set aside.

Heat a grill pan to medium-high heat. Place the pineapple slices on the preheated grill and cook in batches on each side for 3-5 minutes until caramelized and the grill marks show. Be prepared for a bit of smoke form the sugars if you're cooking inside.

To serve, place the pineapple ring in a shallow bowl or plate, top with a small scoop of ice cream or 'nice cream in the centre, and drizzle with the salted caramel.