Caramelized Banana with Rum Sauce

Name: Caramelized Banana with Rum Sauce
Ingredients: 2 teaspoons unsalted butter; 1 banana, halved lengthwise, then crosswise; 2 teaspoons packed brown sugar; 2 tablespoons rum (preferably dark); 2 teaspoons water; 1/8 teaspoon freshly grated nutmeg; 1/8 teaspoon cinnamon; 2 tablespoons sliced or chopped nuts, toasted; Accompaniment: vanilla ice cream