Using a good cooking spray, spray a large grill pan and heat over a medium flame. Grill the pineapple, for 2 to 3 minutes on each side, until it is nicely brown with grill marks. We prefer the barbecue grill as another option.
In a medium saucepan, mix together the brown sugar, butter, heavy cream and dark rum. Allow to boil over medium heat, stirring constantly. Boil for at least 3-4 minutes, continuing to stir constantly until sauce is slightly thickened. Best if served warm. (Sauce can be stored in refrigerator covered for up to 1 week.)
To assemble your Grilled Pineapple Ring Rum Sundae, place a pineapple ring on each serving plate. Scoop a scoop of vanilla ice cream on top of the center. Drizzle your rum sauce across the top. Enjoy!