You can make either the 8" or 6" cake first, the instructions are the same for both, or make both cakes at the same time if you have enough oven space!
Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4, and grease and line two 8" cake tins, and two 6" cake tins (that are at least 2" deep)
Place the dates and boiling water into a bowl and leave them to soak for 15 minutes
Puree the dates and water together using a stick blender or food processor
In a large mixing bowl, weigh out the self raising flour, wholemeal flour, baking powder and cinnamon
In a second mixing bowl, mash up the bananas then add the eggs, vegetable oil and milk. Whisk everything together
Pour the banana/egg mixture into the bowl of flour, along with the date puree, and mix until combined
Stir in the grated apple
Divide the mixture between the tins, using scales for accuracy
Bake the 8" cake for 40-45 minutes or until a thin skewer inserted in the centre comes out clean. Bake the 6" cake for 25-30 minutes or until a thin skewer inserted in the centre comes out clean. Leave to cool fully
To make the cream cheese frosting mix together the butter and cream cheese until combined, then stir in the vanilla and agave nectar
Use a cake leveller or a knife to level off the cake if they have domed at all, or the top of them is not flat
Place the bottom 8" cake layer onto a cake board, plate or cake stand
Spread cream cheese frosting over the cake, then add the second 8" layer and cover the whole cake with the frosting
Insert dowels into the cake (only necessary if you are adding a second 6" tier)
Place the bottom layer of the 6" cake onto a cake board and spread with frosting, then add the top layer. Place the whole 6" cake on top of the 8" cake
Cover the entire 6" cake in cream cheese frosting, making sure to cover the join between the tiers
Add berries of your choice. Please note that cut berries will run their juice into the frosting so don't cut the berries in half if you're not ready to serve the cake yet
Chill in the fridge for 1 hour to firm up the frosting before serving
Store any leftovers in the fridge and eat within 3 days