Swiss Milk Toffee - cooking recipe

Ingredients

2 lbs sugar
1 (218 g) can condensed milk
1 cup milk
1 cup water
butter
vanilla extract (optional)

Preparation

Grease one 7x11 inch baking pan and another of half the capacity.
Put the sugar, condensed milk, milk and water into a large, deep saucepan (I use a pressure cooker pan). Add a walnut sized piece of butter.
Heat the mix gently until all the sugar has dissolved, then bring to the boil.
Reduce the heat and simmer gently, stirring occasionally. It needs to cook for up to an hour, but the colour will change from an unappealing beige to a golden caramel as it cooks, showing it's nearly ready.
The toffee is ready when it reaches the soft ball stage. Use a candy thermometer, or drop a teaspoonful into some cold water.
Half fill the sink with cold water and place the saucepan in it. Beat the toffee with a wooden spoon until smooth and thick. Stir in the vanilla, if using.
Pour the toffee into the baking pans, getting all the really liquid part of it out of the saucepan. (As it sets, white \"blooms\" may appear. These are just milk solids (probably from the butter).
Scrape the toffee that has stuck to the sides of the pan out with a metal spoon. This should give nuggets and flakes of toffee.
When the toffee in the baking pans has set, score and cut into squares.