Two delicious cakes in one! Liam hid a star inside, but you can hide whatever shape suits your occasion. Just remember that it needs to be a little smaller than the depth of the loaf tin.
Heat the oven to 180°C/160°C fan/Gas 4. Make the chocolate sponge. Place the caster sugar, plain flour, cocoa powder, salt and bicarbonate of soda into a large mixing bowl.
In a separate small mixing bowl, combine the coffee, buttermilk, soured cream, vegetable oil, egg and vanilla and whisk together. Stir the wet mixture into the dry to form a smooth, thick batter.
Spread the batter evenly in the traybake tin and bake for 12–15 minutes, until firm to the touch. Leave to cool in the tin for 5 minutes, then turn out onto a wire rack and peel off the paper. Allow to cool completely.
Meanwhile, make the Biscoff sponge. Place the butter, Biscoff spread and caster sugar in the bowl of a stand mixer fitted with the beater and beat until light and fluffy. Whisk in one egg at a time until smooth, then fold in the flour, baking powder, vanilla and milk. Mix to a smooth batter then spread about one third into the base of the loaf tin.
Cut out pieces of cooled chocolate cake using the star-shaped cutter – you’ll need 8 or 9 shapes (or enough to pack tightly along the length of the loaf tin). Place the top of each star downwards, remembering that you’ll invert the cake to cut it. (You will have some chocolate cake left over – top this with a little buttercream, then cut it into cubes and freeze for another day.)
Spread the remaining cake mixture over the shapes in the tin and level the top. There should be no chocolate cake showing through. Bake for about 1 hour, or until a skewer inserted into the centre comes out clean (remember there’s already cooked chocolate cake in there – you want to avoid this). Leave to cool in the tin for 10 minutes, then turn out onto a wire rack to cool completely.
Make the buttercream. Beat the butter and Biscoff spread together in the clean bowl of a stand mixer fitted with the paddle, until smooth. Then, beat in the icing sugar, milk and vanilla until smooth and creamy.
Once the cake has cooled, invert it onto a cake board so that it is upside down with a flat top. Spread the top and sides thinly with the buttercream, adding a thick layer of buttercream at the ends to create a round-ended rectangle. Refrigerate for 15 minutes, to set.
To decorate, roll out the red and green sugar pastes into rectangles measuring about 30 x 7cm, then cut each rectangle into 2.5cm-wide strips. Alternate these along the sides of the cake, and trim at the bottom to neaten. Reserve the red trimmings.
Roll out 100g of the yellow sugar paste into a rectangle large enough to cover the top of the cake. Trim it neatly, then use some of the remaining yellow icing to create a long string and position this to edge the top of the cake neatly.
Mix 1 teaspoon of gold lustre powder with a couple of drops of the alcohol, then use the paintbrush to paint this all over the yellow icing.
Roll out the remaining yellow sugar paste to a rectangle measuring about 12 x 7cm and cut into 1cm-wide strips. Fold each strip in half and use as many strips as you need to create a circular bow on top of the cake.
Roll the reserved red trimmings into a ball and place this in the centre of your bow. Leave to set.
To make the royal icing, put the egg white in the bowl of a stand mixer fitted with the whisk. Whisk for 10–20 seconds at medium speed, then turn off the motor and add some icing sugar. Whisk at a slow speed, gradually adding the remaining icing sugar, increasing the speed as the icing sugar is incorporated.
Use a spatula to wipe any mixture from the sides of the bowl, then add the lemon juice. Keep beating at high speed until you have a piping consistency.
Place the icing in the small piping bag, snip the end to create a small hole and pipe dots all around the edge of the cake and between the colours on the sides. Pipe a ring around the red ball on top.