Heat oven to 180C/160C fan/gas 4.
Grease and line the base and sides of
two deep 23cm cake tins. Boil the
kettle. Put the butter and chocolate
in a small pan and gently heat, stirring,
until completely melted. Mix together
the flour, sugar, cocoa and bicarbonate
of soda with a pinch of salt in your largest
mixing bowl. Whisk the eggs, buttermilk,
orange zest and juice together in a jug.
Scrape the melted chocolate mixture and
egg mixture into the dry ingredients, add
150ml boiling water and whizz briefly with an electric whisk until the cake
batter is lump-free. Divide between the
tins and bake for 45 mins – swapping
the tins round after 30 mins if on different
shelves. To test they’re done, push in
a skewer and check that it comes out
clean. Cool the cakes in their tins.
Meanwhile, make the marzipan. Mix
the sugars, ground almonds and cocoa
in a bowl. Make a well in the middle, tip in
the egg and egg yolk and mix together
with a cutlery knife before kneading with
your hands to a smooth ball. Wrap in
cling film and set aside. Will keep in the
fridge for 1 week if making ahead.
Make the frosting: beat the mascarpone
and butter together until smooth. Sift
in the icing sugar, add the zest and juice,
then beat again until combined.
To assemble, split each cake in half
horizontally. Dot a little frosting on your
serving plate and sit one of the cake
halves on top. You’ll use about half the
frosting to sandwich the cakes together
– spread the plated-up cake with some
frosting, then repeat to sandwich the
remaining cakes on top. Brush the top of
the cake with a tiny bit more frosting.
Roll out the marzipan, on a dusting of
cocoa if you need, to a rough 27cm circle.
Using your cake tin like a cookie cutter,
stamp out a marzipan circle, then
carefully lift this onto the top of your
cake. Roll the remaining marzipan into
11 small balls and stick them on top,
using a little more frosting or water like
glue. Spread the remaining frosting round
the outside of the cake, then dust the top
with a little more cocoa and icing sugar.