Dulce de leche is sugar caramelized with milk, popular in Mexico and in Central and South America. In Latino groceries or pastry shops in the U.S., you see it sold in big brown chunks, wrapped in plastic wrap.

It is a pain in the ass to stand there mixing the stuff for two hours over a double boiler, and I don't have a double boiler, so...

Here is an incredibly easy recipe for dulce de leche.

Take a can of condensed milk, take off the label.
Don't open the can.
Put the can in a pot.
Fill the pot with water so that the can is covered.

Boil for 3 hours.

Check the pan periodically to make sure the can stays covered with water!
You should check the can once in a while to make sure it is not bulging or about to explode.
If it looks bulgy, take it off the heat and let it cool. Then punch a tiny hole in the top and re-boil.

If you only boil it for 2 hours you get a runny dulce de leche, good for an ice cream topping or to smear on toast.