This delicious take on a traditional float features pineapple, vanilla ice cream and a hint of rum. In place of fresh pineapple, you can drain two eight-ounce cans of crushed pineapple, roast it, and skip making the syrup.
Preheat oven to 425 degrees. Peel pineapple using a sharp knife, reserving peels as you work. Cut flesh lengthwise into quarters; cut out and reserve core. Transfer peels and core pieces to a large pot; reserve flesh. Add 5 cups water; bring to a boil. Add granulated sugar and vanilla bean; cook, mashing peels occasionally with the back of a spoon to extract juice, about 30 minutes.
Meanwhile, cut pineapple into 1/2-inch cubes; transfer to a rimmed baking sheet. Sprinkle with brown sugar and rum. Cook until just golden, about 20 minutes. Transfer to a bowl; let cool completely. Cover; refrigerate up to 2 days.
Pour pineapple-peel mixture from pot through a sieve into a large bowl; discard solids. Return liquid to pot, and bring to a boil. Cook until reduced to 1/2 cup, about 4 minutes. Refrigerate syrup, covered, until ready to serve, up to 2 days.
Divide pineapple evenly among 8 serving glasses. Top with 2 teaspoons syrup and 2 scoops ice cream. Fill with club soda. Drizzle with remaining syrup.