Cake Base: Preheat the oven to 180 degrees C. Line a 25cm springform tin with baking paper and grease it.
Beat the egg yolks. Sift the plain flour with cornflour, baking powder and cocoa then fold into the egg yolks. Whisk the egg whites with water, sugar and salt until stiff then fold into the flour mixture.
Bake the sponge in the preheated oven for 40 minutes until a skewer comes out clean. Cool and carefully remove from the tin. Cool completely and cut in half to make two rounds.
Filling: Strain the yoghurt for 30 minutes through a coffee filter or muslin cloth placed in a fine sieve. Drain the tinned fruit retaining the juice.
Sweeten the strained yoghurt with icing sugar to taste.
Mix the juice from the tinned fruits with the gelatine then heat in the microwave to dissolve the gelatine. Place the mix into the fridge for a short while so that the mixture thickens but don't allow it to set.
In the meantime quickly beat the cream until stiff. Fold the cream and lemon juice into the gelatine mixture. Mix the yoghurt with the fruit retaining some fruit for decoration.
To Assemble: Spread the filling over the cake base. Place the second half of the sponge on top of this and pour more filling on top of this.
Decorate with the remaining fruit and place into the fridge immediately. Leave for a few hours in the fridge until the filling has set.