Puree the raspberries in a blender and press through a fine sieve to remove the seeds. Add enough water to make 500 milliliters of puree.
To make the base, place the raspberry puree and sugar in a saucepan over a medium heat. Stir to dissolve the sugar and bring to the boil. Mix the corn flour with just enough water to make a smooth paste. Once the fruit puree reaches boiling point, reduce the heat to low and whisk the corn flour paste into the fruit puree a little at a time. Whisk for 1 minute and do not allow mixture to boil again. Remove from the heat and set aside. Chill to cool completely.
Preheat the oven to 180°C/350°F.
Place the egg whites into a very clean, very large mixing bowl, add the salt and beat at high speed until soft peaks form. Add the sugar, a little at a time, and beat until stiff peaks form. Do not over whisk or the egg whites will break down and be unable to hold the air required to life the souffle.
Place the fruit puree base into a very large bowl and whisk until smooth. Add a little of the egg white mixture and stir in to loosen the consistency. Gently fold in the remaining egg white and rose essence.
Brush the bases of 6 1-cup capacity ramekins with the softened butter, then, using upward strokes (this is very important), brush the sides. Chill in the refrigerator until set, and then repeat. Sprinkle in a little of the caster sugar, turning the ramekins to coat the base and sides. To fill the moulds, use a palette knife to spread the souffle mixture around the sides while holding the ramekin at a 45-degrees angle. Fill the middle and smooth top top, without allowing any mixture to stick to the rim or run over the sides.
Place in the oven and bake for 12-14 minutes or until golden and well risen. Serve immediately dusted with icing sugar, and with creme anglaise or ice cream on the side, if you like.