I promised, here we go.
You can use any condensed milk, but I strongly recommend that if you decide to make dulce le leche, make a lot, because it needs time, and energy (the oven is on 220 C for two hours...)
A middle-sized jar could be filled with two tubes of condensed milk. So if you like caramel, buy a lot, and make it on a cooler day :))
Sweetened condensed milk
Preheat the oven for 220 C.
Put the condensed milk in a heatproof bowl (glass, obviously). Place it in a baking tray. Boil water, and when the oven is ready, fill the tray with boiled water - the top of the water has to be at the half of the heatproof bowl.
Immediately, cover the tray with foil, and put it in the oven. It is going to be ready in 2 hours. In every 1/2 hour, put it out, replace the foil, mix it with a wooden spoon, than put the foil back immediately, and put back in the oven.
When it is ready, let cool completely, than fill it in jars.