Preheat an outdoor grill or grill pan. Grill the pineapple slices until caramelized on both sides. Transfer pineapple slices to a cutting board. Punch out the cores with a 1 1/2-inch round cutter. Place a scoop of vanilla ice cream in the center of the pineapple slices, then drizzle some molasses and sprinkle cinnamon sugar, to taste. Serve immediately.