This is so simple, I feel silly posting it as a recipe. I have always loved this stuff. Sweetened condensed milk cooked for so long that it becomes a rich dark toffee caramel. Its the base for banoffee pie, and to banish sweet cravings, there is nothing better than a teaspoonful.
Most people recommend boiling cans of unopened sweetened condensed milk over the stovetop for 3 hours or so. This is the easiest way to create dulce de leche BUT its also very dangerous. When I was about 13, I was overnighting at an Aunts house in St Johns Wood in London. I was flying out the next day, and she was not there. I was craving something sweet, so decided to make dulce de leche the traditional way. I put my cans of unopened condensed milk in a deep saucepan, and covered with water. And then I proceeded to fall asleep on the couch! I woke up to a HUGE bang and could not, for the life of me, figure out what had happened, until I walked into my Aunts gorgeous gourmet kitchen to find caramel dripping from the ceiling, and every available surface. It took me HOURS to clean up (and I dont think I got everything because a few weeks later, had a very uncomfortable conversation with her!).
Ever since then, I have been a tad nervous about making this. You can pop steam vents into the top of the cans, so that they dont explode, but you still have to check for water every fifteen minutes or so. I prefer this way. Safer, and you can leave it for up to an hour at a time.
Unfortunately, here in Malaysia, we only have sweetened condensed filled milk – which has palm oil as a stabiliser and additive. This method still works, but the preference is obviously for sweetened condensed milk which is just milk and sugar.
You will need one deep roasting pan, filled about 1/3 with cold water, and one smaller roasting pan which can fit inside the deeper one.
Preheat your oven to 170 F.
Place the deep roasting pan into the oven to heat gently.
Pour up to 3 cans of sweetened condensed milk into the second roasting pan, and cover tightly with aluminum foil.
Place this second pan into the first and leave in the oven for up to 3 hours. I would certainly check every hour or so to make sure the water is still there, and to mix the slowly caramelising milk well.
Be careful when you open the oven. A lot of steam gets generated from the water bath, and everything is really really hot.
After about three hours, when you take it out of the oven, dont worry. It will look curdled and lumpy. Some bits will be dark caramel brown, some bits will be lighter and smoother, and some bits will look like milk curds. Just pour and scrape into a clean bowl, and beat with a wire whisk until smooth. Let cool before even thinking of tasting it!
You can flavour this with some vanilla if you like. Unspeakably delicious.
delectable 
It exploded? Wow, I will definitely take this tip from the top, P!
Literally, sticky hot caramel dripping everywhere. And that stuff is boiling when it comes out the can, so it can be very very dangerous!