Pre-heat the oven to 160°C(fan). Line a 20 cm deep cake tin with parchment paper and grease the sides with butter, then dust with plain (all purpose) flour. Shake off the excess.
Sift the flour and to set one side. Melt the butter in a small saucepan, pour into a medium bowl and set to one side to cool to room temperature.
In a free-standing mixer with a whisk attachment, beat the eggs and sugar on a high speed until you reach ribbon stage. This will take a good 5 minutes, set a timer as this is crucial because there is no raising agent in this cake.
Pour half of the flour over the egg mixture and then, this is important, use a balloon whisk to fold it in, repeat with the remaining flour. Now whisk approximately 3 tablespoons of the cake batter into the butter, this really helps to incorporate the butter into the batter. Now whisk in an additional tablespoon of batter into the butter mixture. Fold the butter mixture into the batter with a spatular until it’s just combined. Don't over mix or you'll knock the volume out of the cake.
Pour into the prepared tin and bake for 30-32 minutes or until a cocktail stick inserted into the centre of the cake comes out clean. (The sponge will shrink away from the tin when it's fully baked).
Now for the crème pâtissière, in a large bowl whisk the egg yolks, sugar, vanilla extract and cornflour together until pale and creamy. Pour the milk into a pan and place over a medium-low heat until just simmering. Whisk the warm milk into the egg mixture. Pour the mixture back into the pan and cook over medium heat for 4-5 minutes, whisking until the mixture boils and thickens.
Remove from the heat and beating the butter into a the mixture and then transfer to a bowl and cover the surface with a disc of parchment to stop a skin forming. Chill in the fridge until needed.
Combine the jam with the fresh or frozen raspberries and set to one side.
To assemble: with a serrated knife, cut the cake horizontally into three layers. Spoon the jam mixture onto the bottom layer of the cake now place the middle layer of the sponge on top. Remove the the creme patisserie from the fridge and whisk vigorously until smooth. Spoon this onto the middle layer of the cake. Now place the final layer of sponge on top of the crème pâtissière. Whip the cream until stiff peaks form. Spread a generous layer on top of the cake using a palette knife and cover the cake with a thinner layer around the edges. Place the cake in the fridge to set while you roll out the marzipan.
Now to colour the Marzipan, I have used a natural food colouring here. Just add a little to a small amount of marzipan, kneading it in to distribute the colour, then add this to the uncoloured marzipan, you have to work at distributing the colour and it takes a little time. once this is done roll the marzipan out until it’s at least a third bigger than the cake.
Place the marzipan disc on the cake and gently cup your hands around it to shape it smoothly over the sides. Use a small, sharp knife to trim the excess at the bottom for a clean edge. If this proves challenging, roll out any remaining marzipan and create a band to place around the bottom.
To decorate: pipe with dark chocolate, and dust with icing sugar and finish with an edible flower or two.