Method 
1. Preheat oven to 180°C.
2. Place rhubarb in a saucepan with 75g of the caster sugar and ¼ cup water. Cover and place over medium heat and cook for 5-10 minutes until softened. Add blackberries and lemon zest and cook, uncovered, for 5 minutes until softened. Add ½ of the cornflour mixture and stir for 3-4 minutes until thickened, then cook for a further minute to cook out the cornflour. Set aside in a bowl to cool to room temperature for at least 5 minutes.
3. Meanwhile, to make the crumble topping, combine flour, 50g of the butter, sugar and a pinch of salt in a bowl, mixing with your fingers until combined and the butter is in pea-sized lumps. Add the oats and hazelnuts and toss gently to combine.
4. Place the crumble mixture on a lined baking tray and bake for 5 minutes until golden brown. Remove from the oven and set aside. Increase oven temperature to 200°C.
5. Grease 125ml soufflé moulds with remaining butter that has been slightly softened. Butter base and sides with a pastry brush, then brush up the sides – you want an even coating of butter. Refrigerate for 5 minutes to set the butter, then repeat the process - for the second buttering, be a bit more generous with the butter. Sprinkle sugar into each mould and roll ramekin around so the sugar coats the butter, tipping out any excess. This forms a lubricated crust so the soufflé can rise easily.
6. Place egg whites in a large, clean, dry bowl with 1 tablespoon of the remaining sugar and beat with a hand beater on high until soft peaks. Gradually sprinkle in the remaining sugar and beat for about 30 seconds - 1 minute until you have shiny, soft peaks.
7. Mix an equal amount of beaten egg white with cooled fruit puree until combined, then add the same amount of egg white again and fold through gently, turning the bowl, then lifting and folding the mixture to keep as much air in the mixture as possible. Spoon into buttered, sugared moulds, taking care to avoid getting any mixture on the side of the ramekins until the moulds are full. Scrape the mixture off the top with a palette knife so you have a really smooth surface, then run your thumb around the very inside of the rim so you have a clean rim.
8. Bake for 6-7 minutes until risen about 1 cm above the rim. Sprinkle 1 tablespoon of the crumble topping over the top and return to the oven for another 3 minutes until they have risen another centimetre.
9. Serve with vanilla ice cream and a dollop of thick cream.
Makes 6-8 souffles
