Preheat oven to 180ºC. Grease well and line two 23cm sandwich cake tins with baking paper.
Beat egg whites until stiff peaks form. Slowly add Chelsea Raw Caster Sugar (or if using Chelsea Raw Sugar, blitz the raw sugar in a food processor until a finer crystal size is achieved) and beat until mixture is stiff and glossy and the sugar has dissolved. Add the yolks one at a time, mix in well.
Sift together cornflour, custard powder and baking powder. Gently fold dry ingredients into the mixture using a metal spoon.
Pour equal amounts of the mixture into each prepared tin. Bake for 15 – 20 minutes (make sure you don't open the oven door whilst cooking). The cakes should shrink slightly from the sides of the tins and spring back when gently touched.
Cool for 10 minutes in the tin then turn out onto a wire rack covered in a clean tea towel or paper towel to prevent a rack imprint on the sponges.
When cool, fill with whipped cream and fruit and sprinkle with a fine dusting of Chelsea Icing Sugar.