1. Heat your oven 200°C/Gas 6 and butter four ramekins. Put ½ tbsp caster sugar in each ramekin and rotate the dish so the sugar coats the base and the sides evenly. Tap out any excess.
2. Tip the custard and mango purée into a bowl. Cut the passion fruit in half, then scoop out the seeds and juice into the bowl. Mix with the custard and mango purée until evenly combined.
3. Whisk the egg whites in a clean bowl until stiff. Gradually add the 20g sugar, a spoonful at a time, whisking well between each addition, to make a smooth, glossy meringue. Gradually fold the meringue into the passion fruit and mango custard, using a large metal spoon or spatula, until it is all incorporated.
4. Divide the mixture between the prepared ramekins. Use a palette knife to gently smooth and level the surface of each soufflé, then run your finger around the edge to lift the mixture away from the side slightly (this helps it to rise evenly).
5. Bake for 12-15 minutes until the soufflés are risen. Dust with icing sugar and serve immediately.