Separately, mix the dry and wet ingredients well. Pour the resulting mixture into a form with a diameter of 9″ (24 cm), in which you've placed baking paper beforehand. Bake in a preheated 320°F (160 °C) oven for 20 minutes.
Once cool, cut it lengthwise into two halves and stick them back together with the buttercream.
Prepare the white cream by first melting the chocolate bars in a water bath. Leave to cool and add the gently beaten with a mixer cream. Whisk it and spread it along the entire cake. With an icing piping syringe, make florets topped with diced cocoa biscuits and grated chocolate, if desired.