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.
Slice bananas diagonally.
Add to brown sugar mixture in skillet, tossing to coat.
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.
Bake at 450 for 10 minutes or until bubbly.
Remove from oven, and sprinkle evenly with biscotti crumbs.