2 firm-ripe bananas, thinly sliced crosswise
1 cup sour cream
2 teaspoons vanilla
1/4 cup brown sugar
Special equipment: 4 (6- by 4-inch) gratin dishes or 1 (1- to 1 1/2-qt) gratin dish
Preheat broiler. Divide bananas among gratin dishes. Stir together sour cream and vanilla in a bowl, then spoon over bananas, covering them and smoothing tops. Sprinkle each gratin with 1 tablespoon sugar and broil on a baking sheet 3 to 5 inches from heat until sugar is melted but not caramelized, about 3 minutes.