Step 1. Prepare the Baking Dish

Lightly grease a 9×9-inch baking dish or line it with parchment paper, allowing some overhang for easy removal later.

Step 2. Melt the Mars Bars and Butter

In a saucepan over low heat, add the chopped Mars bars, butter, and golden syrup. Stir continuously until the mixture is fully melted and smooth. Be careful not to overheat, as the chocolate can scorch.

Step 3. Add the Rice Krispies

Remove the melted Mars bar mixture from the heat. Gently fold in the Rice Krispies, mixing until they are well coated with the chocolatey caramel mixture.

Step 4. Press into the Baking Dish

Pour the Rice Krispies mixture into the prepared baking dish. Use a spatula to press the mixture down evenly, creating a firm layer. Place in the fridge for about 15-20 minutes to set slightly.

Step 5. Melt and Pour the Chocolate Topping

While the base is setting, melt the milk or dark chocolate in a microwave-safe bowl in 20-second intervals, stirring in between, or over a double boiler. Pour the melted chocolate over the Rice Krispies base, smoothing it out with a spatula to cover evenly.

Step 6. Chill and Serve

Place the baking dish back in the fridge for at least 1 hour or until fully set. Once firm, remove the cake from the dish using the parchment overhang, cut it into squares, and enjoy!