Preheat the oven to 180C/350F/Gas 4. Grease two ramekin dishes with butter and sprinkle with one tablespoon of the caster sugar.
Place the egg whites into a large clean bowl and whisk until stiff peaks form when the whisk is removed. Add the remaining sugar and whisk again until thick and glossy.
Place the custard into a separate large bowl, add the passionfruit seeds and pulp and mix well. Gently fold in the whisked egg whites. Spoon the mixture into the prepared ramekins and place onto a baking sheet.
Transfer to the oven and bake for 15-20 minutes, or until risen and golden-brown.
Meanwhile, for the bananas, heat the butter in a non-stick pan until it turns slightly brown. Add the sugar and the bananas and cook, stirring frequently, until the bananas are golden-brown all over.
To serve, place the soufflés onto serving plates in their ramekin dishes. Place the bananas alongside and serve with a scoop of vanilla ice cream. Garnish with fresh mint.