Line an 8 or 9 inch square baking tin with baking paper and set aside.
Roughly chop up 5 of the mars bars and add them along with the butter and golden syrup to a large saucepan over medium heat.
Stir constantly while heating to melt everything together. If it starts to bubble, remove from the or turn the heat down to low and keep stirring.
Once it’s all melted add the vanilla and salt and stir to combine .
Add the Milo cereal and stir until all the cereal is coated.
Tip everything into the tin and press down with the spatula all over, pushing it right into the corners and edges. If cool enough you can use your hands. Make sure there aren't too many gaps in the top layer or the chocolate you top them with will escape.
Chill at least 1 hour.
Place the chocolate in a microwave safe bowl and melt in the microwave in 20 second burst, stirring really well between each. This should only take 1 minute. No longer or you risk burning it.
Pour it over the cold mars bar slice. Finely slice the last mars bar and place them randomly all over the top.
Let it set in the fridge for 1-2 hours before cutting into small pieces and serving.
I use a standard Australian 20ml tablespoon (equivalent to 4 teaspoons)
Cut the pieces small if using Milo cereal so that it's easier to bite into (Milo cereal is extremely crunchy)