You can make your own dulce de leche with a single can of sweetened condensed milk. To do so, bring a large pot of water to boil and place the entire unopened can in the water. Allow the can to simmer on low heat for 2-3 hours (2 hours = lighter dulce de leche, 3 hours = darker dulce de leche), flipping the can halfway through carefully with tongs. Pull the can out of the water and allow it to cool at room temperature. Open the can and you'll have perfect dulce de leche!