Dulche de leche is a caramelized milk and sugar concoction which tastes divine and has become a traditional South American, or more precisely Argentinian, treat. Unlike fudge or toffee, where the colour and flavour come from caramelized sugar, it is the milk proteins which are changed resulting in the smooth, delightful taste and texture of dulche de leche.
Legend has it that dulche de leche was discovered by accident in 1829 when an Argentinian servant forgot about a pot of milk and sugar which was left simmering on the fire. The resultant sticky goo was the found to be delicious and from that day forward was incorporated into the diet served with bread, fruit, toast or desserts. It goes wonderfully well with pineapple or bananas; banoffee pie is a quick and easy dessert where sliced bananas (dipped in lemon juice to preserve the colour) are layered into a biscuit base covered with generous amounts of dulce de leche.
The methods above are the more conventional way to make dulce de leche, but by far the quickest way is to use a pressure cooker. One or more cans of sweetened condensed milk (not evaporated milk) can be placed on a trivet in the pressure cooker and steamed at 15lb pressure for approximately 40 mins - 1 hour, depending on how dark you want it to be (believe me, they don't explode!). Let the pressure come down naturally, and allow to cool. The tins can be stored unopened for as long as your willpower holds out, or, if not, open one as soon as it's cool enough to handle, and spoon it straight from the tin!
Vorbis says "Maybe you should append to your writeup the theory that Dulce de Leche spontaneously evaporates even when put in tightly sealed jars. Either that, or the spirits that haunt my refrigerator are particularly hungry." This is so true - I recommend sealing the jar with a band of garlic cloves to keep away the sweet-toothed goblins!