Line a 22cm square baking tin.
In two large thick bottomed pots, combine the chocolate chips, condensed milk and butter for each of the fudge recipes
Stir over medium heat until mixture is evenly melted and smooth.
Cook, while stirring, over medium heat for 2 minutes – the white chocolate will need to cook for an extra 5 minutes.
Pour dark chocolate fudge into the prepared tin first, then the white chocolate fudge on top.
Using a spoon, swirl the fudge to make a marbled effect.
Refrigerate until firm before slicing into blocks.