The banana custard can be made up to 1 day ahead, covered and refrigerated. Bring to room temperature before proceeding.
Unsalted butter, for the ramekins, at room temperature
4 1/2 Tbsp caster sugar, plus more for the ramekins
2 large ripe bananas, unpeeled
2/3 cup cream, at room temperature
2/3 cup milk, at room temperature
1/2 vanilla bean, split lengthwise
3 large eggs, separated
3 tsp plain ?our
2 large egg whites
Icing sugar, for dusting
3/4 cup Caramel Sauce (recipe follows)
Position a rack in the centre of the oven, place a heavy baking tray on the rack, and preheat the oven to 190°C. Completely coat the interiors of four 250ml ramekins (9cm diameter) with some of the butter, with your brush strokes going from the bottom of the ramekins to the top (this will help the soufflés rise better). Refrigerate for about 2 minutes, or until the butter is cold and set. Brush with a second coating of butter in the same manner, then coat the interiors with caster sugar and shake out any excess sugar. Refrigerate the ramekins.
Place the bananas on a baking tray lined with foil and roast for about 30 minutes, or until the banana peels are completely blackened and the flesh is soft. Remove the bananas from the oven (leave the oven on).
Peel the bananas (you should have about 1 heaped cup of banana flesh). Transfer to a blender, add the cream and milk, and puree until smooth.
Transfer the banana mixture to a medium heavy saucepan. Scrape the seeds from the vanilla bean into the mixture and bring to a simmer over medium heat.
Meanwhile, in a medium bowl, whisk 1 1/2 tablespoons of the caster sugar and the yolks for about 1 minute, or until light and fluffy. Whisk in the flour, then whisk in the hot banana mixture. Return the mixture to the saucepan and cook, stirring constantly, over medium-high heat for about 2 minutes, or until the custard is very thick and just
beginning to bubble.
Transfer the custard to a large bowl, press a sheet of plastic wrap directly on the surface of the custard to prevent a skin from forming, and cool for 30 minutes, or to room temperature.
In the bowl of a stand mixer fitted with the whisk attachment, whisk the egg whites on medium-high speed for about 1 minute, or until they begin to foam. Slowly sprinkle in the remaining 3 tablespoons of caster sugar and beat for about 3 minutes, or until peaks are nearly stiff and still moist. Alternatively, you can use a handheld mixer instead of a stand mixer, but mixing times will be a bit longer.
Whisk one-third of the whipped egg whites into the banana custard to lighten it. Fold in another one-third of the egg whites, then fold in the remaining egg whites. Divide the mixture evenly among the prepared ramekins.
Bake the soufflés for about 15 minutes, or until they have risen but are still a bit liquid in the centre. Dust with icing sugar and serve immediately, with the caramel sauce.