Deadly Chocolate Fudge

Ingredients
1/4 pint double cream
1/4 pint milk
4oz butter
1 lb granulated sugar
3 1/2 oz dark chocolate
NB: The higher the cocoa content and lower the sugar content of the chocolate, the nicer this will be.

Method
Put everything except for the chocolate into a very large pan (trust me) and heat gently, stirring until the sugar has dissolved. Once the sugar has dissolved, bring the mixture to a rolling boil. (A rolling boil is when the mixture doesn't stop bubbling when you stir it)
The mixture is "cooked" enough when:
You get a bowl of cold water, and when a teaspoon of the mixture is dripped into the water it goes into a "soft ball" - Although unless your bowl is deep, it's more like a soft gooey blob.
Pour the mixture into a 20x20cm tin which has been well greased and put it into the fridge.
Once it has set cut it into squares.

Note: This fudge is not actually deadly, that's just a funny name.