Preheat the oven to 425 degrees. Peel the pineapple using a sharp knife, reserving the peels and core as you work. Go here for a tutorial on cutting up a pineapple. Cut the pineapple flesh into 1/2-inch cubes. Transfer the peels and the core pieces to a large pot; reserving the cubed pineapple flesh.
Add 5 cups of water to the pot and bring to a boil. Add the granulated sugar and vanilla extract. Cook for about 30 minutes, mashing the peels occasionally with the back of a spoon or a potato masher to extract the juice. You won’t actually see the pineapple peels “give” at all – but mashing still helps to release the juice.
Transfer the cubed pineapple to a rimmed baking sheet. Sprinkle the pineapple with the brown sugar. Cook until just golden, about 20 minutes. Transfer to a bowl and let cool completely. Cover and refrigerate for up to 2 days (or use immediately once cooled).
Pour the pineapple peel mixture from the pot through a fine mesh strainer into a large bowl. Discard the solids and return the liquid to the pot. Bring the liquid to a boil and cook until reduced to 1/2 cup about 10-12 minutes. Refrigerate the syrup, covered, until it is ready to serve, up to 2 days.
When ready to serve, divide the pineapple evenly among the 8 serving glasses. Top with 2 teaspoons syrup and 2 scoops of ice cream. Fill with club soda. Drizzle with remaining syrup and serve. I garnished the glasses with a few chunks of pineapple skewered on a wood stick.
Notes
Pineapple: in place of the fresh pineapple, you can drain two 8-ounce cans crushed pineapple, roast it, and skip making the syrup.