Remove the label rom your can. You can use more cans if you'd like more dulce de leche, you're just limited by the space In your pot.
Place can(s) In a pot large enough to accommodate them. Fill with water so the cans are submerged by 1-2 inches and place over medium high heat. As soon as the water comes to a boil reduce to a simmer then just keep an occasional eye on the water level and refill as necessary. 2 hours of simmering will give you a light golden color while 3 will yield a darker amber color with a richer flavor.
Method 2: Baking
Preheat oven to 425F. Pour your sweetened condensed milk into a pie dish or cake pan and cover tightly with foil. Transfer to a deep roasting pan and fill with hot water so you have about an inch of depth.
Bake for 1 hour 45 minutes. You can add or subtract bake time depending on the depth of color desired. Allow to cool and whisk to smooth out and get rid of any lumps.
If you're boiling the cans it's important to monitor the water level, you want them to stay submerged.
Your dulce de leche will last about two weeks in the fridge if kept in a sealed container or three months if left in the unopened can.
If you're employing the boiling method it's better to use the cans that do not have tab openers.