Pre-heat your oven to 160C Fan/350F/Gas Mark 4, and grease and line two 8" cake tins (that are at least 2" deep)
Make the sponge by mixing the baking spread and dark brown sugar together in a mixing bowl until fluffy (around 3 minutes), ideally using an electric mixer. Or mix in a stand mixer with the paddle attachment
Add the eggs and milk, and mix until fully incorporated
Add the self raising flour, cocoa powder, bicarbonate of soda, baking powder, ground ginger, cinnamon and mixed spice, and whisk or fold in gently
Divide the mixture between the tins, use scales for accuracy if you like
Bake them for 35-40 minutes or until a thin skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or remove from the tins and place on cooling racks
To make the buttercream mix the butter on it's own until it's smooth and creamy, for 2-3 minutes. Use an electric whisk or stand mixer with the paddle attachment for best results
Add the icing sugar, orange extract and milk. Mix until smooth. If the buttercream is too stiff then you can add a little more milk
Divide the buttercream equally between three bowls, use scales for accuracy if you like
Colour one bowl of the buttercream red, the second yellow and the third orange. Do this by adding the food colouring to the buttercream and mixing it in with a silicone spatula or a spoon
Place a piece of clingfilm onto your work surface that's around 35cm x 25cm. Lay each colour of the buttercream out in rows in the centre of the clingfilm, making sure that the rows of buttercream touch each other. Roll the cling film around the buttercream and create a sausage shape, twisting the excess cling film at either end
Use scissors to cut open one end of the cling film sausage, exposing the buttercream, then feed that end of the sausage into a piping bag fitted with a nozzle
If the cakes have domed on top, level them off with a cake leveller or a sharp knife
Put one of the sponges on your plate or cake stand and pipe some of the buttercream onto it
Add the other sponge on top and pipe the remaining buttercream on top
Decorate by snapping or cutting each of the orange chocolate sticks into three and arranging them around the outer buttercream swirls
Leftovers will keep in an airtight container in a cool place for 3 days