In a small bowl add the spiced rum and brown sugar and mix until sugar is dissolved.
Place the pineapple spears in a shallow baking dish and pour the brown sugar and rum mixture over top. Cover and ace in the fridge for 2-4 hours flipping once halfway through to coat the other side with the rum mixture.
Over medium-high heat preheat a grill pan or BBQ grill. Add the pineapple spears perpendicular to the grill grates so you can get those nice brown grill marks across the pineapple. Grill for about 3 minutes per side.
Meanwhile, pour the rum mixture left in the baking dish into a small saucepan. Bring to a boil over medium-high heat and cook until slightly thickened and reduced to about ⅓. Remove from heat and stir in the butter, cinnamon and salt. Set aside.
Place 2-3 spears of pineapple on a plate and add a scoop of vanilla ice cream. Drizzle the Cinnamon Rum Sauce over top and serve.
Nutrition calculations based on a 1/2 cup ice cream scoop per serving.