Bottom line is that this is simple and I like it. All you need is a can of sweetened condensed milk. While I was not so brave as to boil it unopened, it seems that I yielded the same ideal result from a slightly vented can.
Get ready to take notes! (Ummm… not at all, actually.) Take the label off of the can and open it just a crack. Put the can in a pot and fill with water, to about 1 inch from the top of the can. (It looked like the can was going to rust my pot, so I put the can on a bed of parchment paper.. you could probably also use a silicone can topper or an enameled pot. Just a thought.) Bring to a boil, then turn down the heat and allow the water to simmer around the can for 2-4 hours (for a softer or harder caramel). I went with the middle ground of 3 hours.
You will need to top up the water throughout the process. And let the can cool (I just left it in the water until the next morning) before trying to handle it. Open the can and scoop out your beautiful caramel coloured confection. Give it a quick stir to remove any lumps but that is absolutely it. Presto: dulce de leche!
Now, what do you do with it?! I used it as a macaron filling and made dulce de leche buns (think cinnamon buns but with dulce de leche instead). You could make tarts. Or just use it as a sweety treaty spread on a piece of bread. Yum yum yum.