Grease and line two 18cm (7 inch) loose-bottomed cake tins
Preheat the oven to 180ºC (160C fan assisted).
Put the caster sugar, eggs, oil, milk and golden syrup in a bowl. Whisk together.
Add the self-raising flour, cocoa powder and bicarbonate of soda. Whisk again to a smooth batter.
Spoon into the prepared tins.
Bake for about 30 minutes until firm and springy on top. Cool in the tin for 10 minutes, then remove from the tin to cool completely.
Make the ganache frosting
Put the dark and milk chocolate in a bowl. Melt gently in 30 second bursts in the microwave.
Pour in the cream and whisk gently until you have a thick, glossy ganache.
Assemble your KitKat cake
Place the first completely cool cake on a board. Spread with about one third of the frosting.
Place the other cake on top and spread the top with another third.
Use the remaining frosting to coat the sides. Aim to get it as level as possible but don't worry about being too neat as you'll be covering it with KitKats and candy.
Stick the Kitkats all the way around the cake. I keep mine in pairs of fingers to speed the work up.
Pour the Smarties (or M&Ms/Skittles) onto the top of the cake, filling to give an even layer. They don't need to reach the tops of the Kitkats.
Place in the refrigerator to firm up for at least an hour before serving.