Put the chocolate, butter, and golden syrup in a heatproof bowl. Microwave in 30 second bursts until completely melted. If not using a microwave, place over a pan of simmering water and stir until melted.
Pour the cornflakes into the melted chocolate and gently stir to coat all the cereal.
Place 12 cupcake cases in a muffin pan and spoon the mixture into the cases. Place in the fridge to set for 30 minutes.