Make the pineapple salad: Toss the pineapple, mint, lime juice and superfine sugar in a large bowl. Cover and refrigerate until ready to serve.
For the custard, first prepare an ice bath. Place the milk in a large metal bowl set over a saucepan filled with 1 inch water. Slice open the vanilla bean lengthwise, scrape the seeds into the milk and discard the pod. Stir to combine.
Heat the double boiler over medium heat until the milk is steaming but not boiling. Turn off the heat. Combine 1/4 cup of the warm milk with the egg yolks in a small bowl, stirring constantly. Add another 1/4 cup of milk, stirring constantly to warm the egg yolks. Pour the egg-and-milk mixture into the remaining milk in the double boiler. Stir in the granulated sugar. Turn on the heat to medium and cook, stirring constantly, until the mixture thickens slightly, about 10 minutes. (The custard should thickly coat the back of a wooden spoon.)
Remove from the heat and put the metal bowl in the ice water bath. Stir in the nutmeg. Stir the custard from time to time until it becomes very cold. When the custard is cold, drizzle some over each serving of pineapple salad and serve the extra custard on the side.