Preparation

• Start preparing the revisited mimosa cake from the base, i.e. the sponge cake. Follow the sponge cake recipe here.

  While the sponge cake bakes, prepare the pastry cream. In a small saucepan put the egg yolks with the sugar and the lemon zest, then whisk together with a manual whisk. Add half of the milk in a thin stream and, little by little, incorporate the sifted flour and starch. Finally add the remaining milk, also in a thin stream, continuing to whisk.
  Place the saucepan over low heat and bring to a boil, stirring gently and continuously. As soon as it reaches a boil the cream will start to thicken: at this point turn off the heat and let it cool completely.
  The sponge cake must also be completely cold before assembling the mimosa cake.
  Meanwhile, you can prepare the whipped cream. I recommend keeping it in the fridge for at least 12 hours before whipping it, so it will be firmer and more stable.

• Now move on to assembling the cake. Cut off the top of the sponge cake, at most about 3/8 inch thick, and set it aside: it will serve as the lid. Score the edges leaving them about 3/16 inch thick and scoop out the center of the sponge with a spoon or small spatula, removing all the interior without breaking the bottom. Crumble the removed sponge and set aside.
  In a bowl combine the pastry cream with half of the whipped cream and work with a whisk until you obtain a smooth diplomat cream.
  Brush the base and the sides of the sponge cake with milk, without overdoing it to avoid sogginess. Fill half of the cavity with the diplomat cream, then distribute the white and dark chocolate chips over it and cover with the remaining cream, leveling up to the top of the edges.
  Cover with the sponge disc set aside at the beginning and spread a thin layer of whipped cream over the surface.
  Finally, cover the entire cake with the crumbled sponge kept aside.
  Let rest in the refrigerator for at least 2 hours before serving.