Whisk the cream until thick.
Cut both cakes into two so you are left with four layers. Place one layer bottom down on a plate or cake dish. Take the pastry cream and cover the sponge, being careful to not go right up to the edges and not to use too much (it will squeeze out of the sides when you add the further layers).
Place the second layer on top and spread over just enough jam to cover the whole cake (again, don't go right up to the edges or use too much). Top with some whipped cream, smoothing it over to make it even. Push the cream over the edge of the cake and using a little more, cover the sides of both layers.
Take a third layer and place on top. Cover with a thin layer of vanilla cream, followed by a thin layer of jam.
Top with the last layer. Cover the top and sides with cream, smoothing as you go (you need the sides to be as level as possible, but perfection is not necessary). Then, pile more cream on top (in the middle) to create a dome shape. Place in the fridge for a couple of hours to firm up.
When ready, cover the cake with the marzipan lid. Attach your decoration and sprinkle with icing sugar. Slice and enjoy your celebrations