Makes 4 to 6 servings, or about 6 cups of ice cream.
Place 1/2 cup water in a small saucepan. Sprinkle the gelatin over the water and allow softening, about 2 minutes. Cut the vanilla bean in half lengthwise and scrape the seeds into the water mixture using a paring knife. Add the empty vanilla pods. Stir the water mixture over medium heat until the gelatin has dissolved. Set aside to cool slightly. Remove and discard the vanilla pods.
Beat the cream until thick using an electric hand mixer in a medium bowl. Add the sugar and continue to beat until the cream holds soft peaks. Add the water mixture, coconut milk and rum. Beat until thick and light.
Pour the mixture into an 8-by-8-inch glass baking dish. Freeze until the mixture is the texture of soft-serve ice cream, about 2 1/2 hours.
Scoop the mixture into small glasses using an ice cream scoop. Garnish with toasted coconut and serve. Freeze any unused ice cream in an airtight container.
Cook’s Notes: To toast coconut, place sweetened or unsweetened, shredded or flaked coconut in a single layer on a baking sheet. Preheat oven to 375ºF. Bake, stirring occasionally, until golden brown, 5 to 10 minutes.
If freezing the ice cream for longer than 2 1/2 hours, allow the ice cream to stand at room temperature until softened, about 30 minutes before serving. Whisk the ice cream until smooth and serve.