Preheat broiler. Peel bananas and slice them crosswise into 3/4-inch thick slices. Mix the brown sugar and lime juice and toss this with bananas. Spread the sliced bananas in a shallow baking pan and broil, as close to the heat source as possible, until the sugar has melted into a glaze - 2 to 3 minutes. Transfer to a pretty serving bowl and serve immediately - topped with sour cream and nuts if you wish.