Stir together the yogurt and cream with the rum, if you’re using it, and whisk until slightly thickened.
Slice the banana and then divide the slices between two one-cup ramekins to form a layer at the bottom of each one. Spoon the thickened yogurt and cream mixture filling the ramekins equally.
Sprinkle 1 tablespoon of sugar over each ramekin, and then wrap them in plastic wrap and refrigerate for a couple of hours, or until sugar has dissolved. Garnish with shredded coconut if desired.