Line a 20cm square cake tin with baking paper - make sure you leave plenty of paper hanging over the sides to help you remove the fudge once it has set.
Roughly chop the Mars Bars into pieces and set aside until needed.
Pour the condensed milk into a medium saucepan over low heat and add the milk chocolate - which has been broken into squares.
Cook condensed milk and chocolate mixture and stir regularly until the chocolate has melted and the ingredients have combined.
Remove the saucepan from the heat and add the chopped up Mars Bars before quickly stirring through.
Pour the fudge into the prepared tin and place in the fridge for a minimum of 6 hours (preferably overnight) to set.
Remove the set fudge from the fridge and cut into squares.