You will need a rectangle silver foil baking tray lined with baking parchment - if you haven't got one of these just line a square or a rectangle tub or a dish with deepish sides.
Melt all the chocolate in one bowl - I do this in 30 second bursts in the microwave, stirring in between each burst.
Melt the butter in another bowl and then add to chocolate. Stir well, then add the icing sugar and condensed milk, and start mixing with a large plastic spoon. It will immediately start to thicken, but keep stirring and don't stop until everything is mixed together and it starts to turn into one big lump. Quickly put it in the lined tin and flatten it out as much as possible.
Leave to set, preferably overnight in the fridge, covered in cling film. When set, tip out on top a chopping board, peel off the baking parchment and cut into strips. Cut each strip into six big chunks. Store in fridge if not eating straight away. Keeps for up to a week.
For the chocolate I use Aldi's Dairyfine, 89p for 200g - fab! If you want creamy coloured fudge instead of dark fudge, use white chocolate with a little milk chocolate. I make this at Easter, Christmas and Halloween and put 12 pieces in small clear plastic sweety bags tied with gorgeous ribbon! Makes great teacher presents!