Makes two 1-quart soufflés
Prepare the soufflé molds:
Butter the bottom and sides of molds. Coat the inside surface with sugar.
Preheat oven to 350 degrees.
In a bowl, combine the bananas, sugar and rum. Let macerate at room temperature for 1/2 hour.
In a medium saucepan, melt the butter, stir in the flour, and whisk in the milk. Stir over medium heat till thick. Stir in the vanilla and sugar. Continue to cook over low heat for 5 more minutes.
Transfer to a large bowl. Cool mixture for 20 to 30 minutes. Mix in the egg yolks one at the time. Blend in the banana mixture.
Beat the egg whites with the cream of tartar until medium-firm. Fold into the banana mixture.
Spoon into the soufflé dishes. Bake for 35 to 40 minutes.