Preheat your oven to 425°F. Bring a kettle or medium pot of water to boil.
Pour condensed milk into a small to medium baking dish like a 6-inch cake pan, loaf pan, or pie tin. Cover tightly with foil, making sure the foil is not touching the milk.
Place a sheet of parchment paper in a second, larger pan like a roasting pan or 9x13-inch baking dish, and set your smaller baking dish on top.
Place pans in the oven and pour boiling water into the larger baking dish until it comes halfway up the side of the smaller one or at least an inch.
Cook for 1 1/2 to 2 1/2 hours, checking every 45 minutes and adding more boiling water as necessary if the water level has dropped too much.
Your dulce de leche is done when it is caramel-colored. Very carefully remove pans from the oven and cool until cool enough to handle or use tongs or a couple of spatulas to remove the smaller dish from the water so it cools more quickly.
Once cool enough to handle, stir dulce de leche until smooth*.
Serve and enjoy!