Line a baking tin with parchment paper and set it aside for later use.
Add butter, golden syrup, cocoa powder and chocolate to a large mixing bowl. Melt over a low to medium heat in the microwave or on the hob until melted.Stop the microwave every 10 to 15 seconds and stir thoroughly.
Put rich tea biscuits into a sandwich bag and bash the biscuits until it forms crumbs and larger pieces.
Place the mini eggs into a sandwich bag and crush the chocolate until it forms broken chunks.
Pour the cornflakes, crushed biscuits and half of the mini eggs into the melted chocolate mixture. Mix thoroughly until the biscuits and mini eggs are fully coated in the chocolate mixture.
Pour the tiffin mixture into a lined 9″ baking tin and press the mixture down using the back of a spoon until compressed.
Sprinkle the remaining crushed mini eggs over the tiffin and gently press it down into the tiffin mixture.
Place the mini egg tiffin in the fridge for at least 1 hour or until set. Depending on your fridge temperature, it may take longer for your tiffin to set completely.
Once set, remove the tiffin from the baking tin and slice it into sections. I usually cut 16 squares.