Line a 23 x 23cm sized baking tray with cling film, lightly grease it with the oil and dust it with 2 tbsp of the corn flour, making sure the base and sides are evenly coated.
Place the gelatine leaves in a small bowl and pour over enough cold water to cover. Set aside for 10 minutes.
Weigh the egg whites into a large metal bowl or electric mixer bowl. Set aside. Place the water, sugar and glucose into a small pan over a medium-high heat. Using a sugar or jam thermometer to read the temperature, heat the sugar mixture to 115C. Once it has reached the heat, begin to whisk the egg whites in the whisking bowl, either with a handheld electric whisk or in a freestanding mixer. When the sugar reaches 121C, squeeze the water out of the gelatine, add to the hot syrup and slowly begin to pour the sugar and gelatine mixture into the egg whites, whilst continuing to whisk. Be careful not to let the sugar mixture come in to contact with the beaters. Continue to whisk gently until the mixture has cooled and is thick enough to hold its shape on the beaters – this should take about 15 minutes. Whisk through the chilli flakes and spoon into the prepared tray, smoothing over with a palette knife. Dust lightly with the remaining corn flour and leave in a cool place to set. Once set, cut in to 2cm cubes.
Make the soup. Heat the olive oil in a large casserole pan or saucepan over a medium heat. Add the onion and fry gently for 5 minutes or until beginning to soften. Add the rosemary and garlic and cook for a further 2 minutes. Add the courgettes and sauté for a further 5 minutes. Next add the stock, bring to the boil, then reduce to a simmer and cook for 10 minutes. Pour into a blender and blend until smooth. Season to taste and top up with a little more water if it seems too thick.
Lightly blow torch each marshmallow or pop briefly under a high heated grill until scorched and blistered. Ladle the soup into bowls, top with a marshmallow, some grated parmesan and a sprinkle of the hazelnuts. Serve.