Preheat oven to 180C. Grease and line an 8 inch/20cm sponge cake tin with baking paper.
Whisk the eggs with a stand mixer (or hand mixer) until pale, fluffy and thickened.
Add sugar and beat until completely mixed and dissolved.
Add the cold water and fold with a metal spoon.
Place the salt, cornflour and baking powder in a metric cup, then fill to the top with plain flour
Sieve the dry mixture three times. Gently fold into the wet mixture.
Pour mixture into prepared tin. Bake for 20 minutes or until the cake springs back when lightly touched in the centre. Cool in tin for 5 minutes, then turn onto a wire rack. Remove paper and cool completely.
Slice sponge in half and spread jam over one half of sponge. Top with whipped cream and top with other half of sponge. Dust with icing sugar.