Grease 4 soufflé dishes with the soft butter and sprinkle with a small amount of caster sugar and then place in the fridge to chill.
Prepare the strawberries by removing the stalks and cutting into halves. Place both the raspberries and strawberries into a food processor and blend until you have a smooth consistency.
Add 100g of the sugar to the food processor and continue to blend so that you have a puree. To remove the seeds from the puree rub the mixture through a sieve and into a large saucepan.
Place the cornflour along with 4 teaspoons of water into a small bowl and mix to form a paste and place to one side.
Heat the puree over a medium flame and bring to boil making sure to continuously whisk. Cut the vanilla pod into half and scrape the seeds into the saucepan along with the cornflour paste.
Continue to whisk the mixture until it starts to thicken then remove from the heat and allow to cool. After the mixture has cooled down place in the fridge for around 10 minutes so it chills
Preheat the oven to 200°C / gas 6.
Separate the eggs so you just have the egg whites and whisk along with the remaining caster sugar until it thickens. Add the egg whites to the puree and stir together. Place the mixture into the soufflé dishes and put in the oven for 10 minutes or until they have risen above the rim by half.