Before you sit down to your main course, preheat the oven to 190°C. Grease the insides of four 200ml soufflé dishes, or ovenproof cereal bowls, with the butter, then coat evenly with some of the caster sugar, tipping out any surplus. Place the dishes on a baking tray.
Purée the raspberries by pressing the fruit through a nylon or stainless steel sieve, using the back of a spoon. Stir the kirsch, if using, into the purée.
When you have finished the main course, whisk the egg whites with an electric beater until stiff but not dry, then gradually whisk in the remaining caster sugar. Beat until the mixture is shiny.
Carefully fold the raspberry purée into the egg whites, then spoon the mixture into the dishes and make a swirl on top of each. Leaving space above for the soufflés to rise, cook in the centre of the oven for 12–14 minutes, or until well risen and lightly set.
Remove the soufflés from the oven, sift icing sugar evenly over the top of each and serve with cream.