Preheat the oven to 450 degrees F.
Brush the bottom of a 9" x 13" baking dish with 1 Tbsp. of the butter. Set the pineapple rings in the dish in a single layer.
In a small pot, bring the remaining butter, maple syrup, rum, lime juice and spices to a simmer, and simmer just until the butter is melted. Pour the mixture over the pineapple.
Bake, uncovered, basting the pineapple with the syrup mixture once or twice, for 20 minutes or until the pineapple is tender. Set a pineapple ring on each of 4 plates and spoon over the sauce. To serve, top the centre of each pineapple ring with a scoop of ice cream and garnish with a mint sprig.