Be very careful to stand away from the stove when you add the rum -- the flames will be brief but dramatic.
Peel bananas, and carefully cut in half lengthwise.
In a medium saute pan over medium heat, melt 1 tablespoon butter. Add 2 tablespoons brown sugar, and swirl until dissolved.
Add 2 bananas, cut side down, and cook for about 2 minutes on each side, turning very carefully.
Pouring from a measuring cup, with the pan off the heat, add 1/4 cup rum. Stand back from stove, and return pan to heat. Shake the pan, allowing rum to ignite. Let the alcohol burn off, and again shake the pan, to coat the bananas. Cook until glazed and translucent, about 1 minute longer.
Remove bananas to warm plates, divide sauce between them, and repeat with remaining 2 bananas.
Garnish each banana with a little dab of creme fraiche or sour cream, and serve immediately.
If you prefer not to use alcohol, substitute apple cider. Remove bananas from pan before adding cider; reduce until thick, about 3 minutes. Then return bananas to pan and proceed as directed.