Grease and line an 8x8 inch square pan and leave to one side. I used Wilton Bake Easy and grease proof paper.
Place butter and golden syrup into a small saucepan and place over a low heat, stirring until the butter is completely melted and combined.
Place broken up digestive biscuits into a medium sized bowl and then pour the melted butter mixture over the biscuits. Stir with a wooden spoon until the biscuits are coated in the butter mixture.
Tip into your prepared pan and press into an even layer with a spoon/your hands. It doesn't matter if it's not 100% neat, you'll be covering it in chocolate!
Leave to cool and set slightly, around 20 minutes.
Sprinkle the base with the dark chocolate chips and then place the milk chocolate into a large, heat proof bowl. Microwave in 20 second increments, stirring in between each one, until the chocolate is melted. Alternatively, you can place the bowl over a pan of simmering water and stir until the chocolate is melted.
Pour melted chocolate all over the biscuit base and gently spread until the whole base is covered.
Leave to set for 10 minutes before placing the white chocolate chips into another heat proof bowl and repeating the above microwave instructions until the chocolate is melted.
Spoon the white chocolate over the milk chocolate layer, drizzling it up and down and across to create lines of chocolate. You can drizzle the chocolate in whatever pattern you wish, I just went with vertical lines as I like how they look!
Leave to cool completely, before covering the pan with cling film and placing in the fridge to set completely, around 2 hours.
Once set, transfer to a cutting board and slice into 9-12 bars. I find a warm knife cuts through the Fridge Cake better! Sprinkle with cocoa powder, if desired.
Triple Chocolate Fridge Cake will keep in an airtight container, at room temperature for 4 days, or in the fridge for 5 days.