1. Stir together first 4 ingredients in a 10-inch skillet over medium heat; bring to a boil. Reduce heat to medium-low, and simmer, stirring constantly, 2 minutes. Remove from heat, and stir in butter.
2. Slice bananas diagonally. Add to brown sugar mixture in skillet, tossing to coat.
3. Spoon banana mixture evenly into 4 lightly greased (1- to 1 1/2-cup) gratin dishes or a shallow, lightly greased 1-qt. baking dish.
4. Bake at 450° for 10 minutes or until bubbly. Remove from oven, and sprinkle evenly with biscotti crumbs. Serve warm with vanilla ice cream.