For the banana ice cream, place the bananas and milk in a large bowl and mix to combine thoroughly. Leave to infuse for 1 hour. Pass through a sieve and pour the banana milk into a saucepan with the egg yolks and sugar. Cook over a medium heat, stirring constantly and taking care that the liquid does not boil, until the mixture thickens. Churn the mixture in an ice-cream maker according to the manufacturer’s instructions until the ice cream is just set. Freeze until required.
For the soufflés, grease four large ramekins with the butter and then sprinkle each with the caster sugar. Preheat the oven to 200C/180C Fan/Gas 6 and place a baking tray in the oven.
Mix the cornflour with 1 tablespoon of water in a small bowl. Place the cornflour mixture into a food processor or blender with the bananas and lemon juice and blitz until smooth.
Place the egg whites in a clean, grease-free bowl and start to beat. Gradually beat in the caster sugar until stiff peaks start to form. Slowly fold the banana pulp mixture into the meringue. Spoon into the ramekins and level the tops.
Place the ramekins on the baking tray and bake for 10–15 minutes, or until risen and golden. Leave to cool slightly and then dust with the icing sugar.
For the caramel sauce, melt the sugar in a saucepan over a low heat, swirling the pan constantly until the sugar darkens. Stir in the double cream until combined and then stir in the semi-whipped cream. Stir in the macadamia nuts.
Serve the soufflés immediately, with the banana ice cream and caramel sauce alongside.