Line an 8-inch square tin with baking parchment. In a large microwaveable bowl, melt the butter, golden syrup and chocolate in short bursts, stirring every 30 seconds until smooth. Stir in the crushed biscuits and chopped KitKats until everything is well coated.
Pour the mixture into the prepared tin and press it down firmly, smoothing the top with the back of a spoon. Melt the milk chocolate in 20-second microwave bursts, stirring between each round, then pour it over the base. Spread it evenly and top with festive KitKats and sprinkles.
Place the tin in the fridge for around 3 hours, or overnight, until fully set. Once firm, run a knife under hot water, wipe dry, and slice into neat squares. Enjoy!
