In a saucepan over a medium heat, combine the cherries, lemon juice and half of the sugar and gently cook for 20 minutes until the cherries are soft and broken down. Remove from the heat and purée until completely smooth. Mix the cornflour with the water then add to the mixture.
Preheat the oven to 180 C / Gas 4. Grease 4 individual ramekins and dust with cocoa powder.
In a bowl, whisk the egg whites until stiff peaks form then gradually add the remainder of the sugar. Stir through the cherry mixture. Divide equally between the prepared ramekins.
Bake in the preheated oven for 8 to 10 minutes until risen. Remove from the oven and serve immediately dusted on top with a little cocoa powder.