This cake is made from two large sponges cut into two layers each, so there are four layers inside the cake. Make the sponge cakes one at a time with 4 large eggs, 225g unsalted butter, 225g caster sugar, 225g plain flour and 2½ tsp baking powder in each cake. You might want to make the sponges in advance, in which case wrap them well in cling film to prevent them drying out. Using a small amount of blue gel food colouring, colour 1kg of fondant to cover the cake. Roll this out to a circle of about 40cm diameter and use your rolling pin to carefully lift this onto the cake. Use a cake smoother (or your hands) to smooth the fondant onto and all around the cake. Cut the excess fondant from the base of the cake with a sharp knife.

Put the butter, sugar and vanilla paste into a bowl and beat with an electric hand whisk until light and creamy. Thoroughly beat in the eggCream together the butter and sugar in a large bowl using a wooden spoon until light, fluffy and pale in colour. In a separate bowl, whisk together the eggs and vanilla extract with a fork until smooth. Repeat until it is a four layer sponge cake (sponge, buttercream, jam, buttercream, sponge, etc.). Coat the entire cake in a thin layer of buttercream and smooth with an offset palette knife. To make the buttercream, beat the butter with an electric whisk or table-top mixer until soft. Sieve in the icing sugar, then beat for 10 minutes until pale and fluffy. Add the vanilla, orange extract (if using) and milk, and beat briefly to combine.

Put the butter and sugar into a bowl and beat with an electric hand whisk or in a stand mixer until light and creamy. Thoroughly beat in each egg, one by one. The submarine is made from two pieces of cake. I searched online for ‘Octonauts Gup-A’ and there were loads of images to guide the shape. The bottom cake should be carved carefully with a serrated bread knife into a teardrop shape with a slight curve on the underside. The top cake should be carved into a triangular shape with a slight curve to the top. Using an offset palette knife, spread the chocolate buttercream onto the base sponge around its top edge, up to 4cm in from each side.Take the next two sponges and cut holes in the middle of the cakes, 4cm from each edge. With my cakes, this was a rectangle of 18 x 13 cm and I used a ruler and a sharp knife to make sure the holes were precise. Put the cut-out sponges to one side. This is a really good template for any sort of character cake. Once you have an iced base, you can decorate with any kind of design you like – just do a Google image search for your favourite characters. Add the lemon zest and juice, sift in the rest of the flour and baking powder and fold them in. Be gentle but make sure the mixture is fully combined, including any flour at the bottom of the bowl. Put this into the cake tin, smooth the batter out with an offset palette knife and bake for 45-50 minutes. Sandwich the two layers together with buttercream and add a light crumb coat of buttercream around both cakes. Preheat the oven to 180degrees C / 160degrees Cfan / gas mark 4. Take your rectangular baking tin, line with baking parchment and grease well.

The smaller sponges for the submarine have the same ingredients as the cakes above but baked in a loaf tin, greased and lined with baking parchment. Each cake takes a mix of 2 large eggs, 112g unsalted butter, 112g caster sugar, 112g plain flour, 1½ tsp baking powder and the zest of 1 lemon (plus the juice of half a lemon) in each cake. Sift in the rest of the flour and baking powder and fold them in. Be gentle but make sure the mixture is fully combined, including any flour at the bottom of the bowl. Put this into the cake tin, smooth the batter out with an offset palette knife and bake for 45-50 minutes. Please make sure that there are no brands, logos or anything identifiable on the child's clothes, such as a school jumper.

Preheat the oven to 180oC / 160oC fan / gas mark 4. Take your springform cake tin, line with baking parchment and grease well.