Preheat the oven to 180C, 160C fan, gas 4.
Mix each cake mix separately in bowls with the eggs, oil, water and cake mix gently together and whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy.
Fill each cake tin up to ¾ of the way up. You will probably end up putting a bowl and a little bit into the 20cm tin and using not quite a full cake mix in the smaller cake tin.
Bake in the centre of the oven for 45-50 minutes or until a rounded knife inserted into the centre of the cake comes out clean, then cool on a wire rack.
Trim the top of the cakes so they are flat and place cut side down on a chopping board. Cut each cake into 3. Always have the cut side down when icing, then you will have a very flat, well shaped top.
Spread roughly 1/3 of a pot of icing between each layer and spread the remaining third over the top and down the sides, creating a naked look around the sides by holding a spatula close to the side of the cake scrapping round and removing any excess icing. Chill each cake for 20 minutes after icing it.
Decorate with summer fruits and flowers then dust over the icing sugar to finish