For the Oven Version

1. Preheat the oven to 425 °F. Pour one can of sweetened condensed milk into a glass pie plate or shallow baking dish. Stir in a few flecks of sea salt.
2. Cover the pie plate snugly with aluminum foil. Set the pie plate within a larger pan that has 2-inch sides. If you like, place the pan on a baking sheet to make transferring it in and out of the oven easier. Add hot water to the outside pan until it reaches halfway up the side of the outside of the pie plate. Place in the preheated oven and bake for 1¼ to 1½ hours. Check the mixture during baking, adding more water as needed to the larger pan.
3. Remove the foil. The dulce de leche should be a medium caramel color. If it is too light in color, it is not ready, so continue to cook it. Remove from the oven and take off the foil. When cool enough to handle, take out of the water bath and let the mixture cool. The mixture will thicken as it cools. Once cool, use a wire whisk to smooth out the mixture. Store in the refrigerator for up to 2 weeks.

For the Stovetop Version

1. Make sure to use a heavy stainless steel or enamel pot like a Le Creuset brand. Other types of pots can cause the sugar to crystallize on the pot side.
2. Heat the mixture until it just begins to boil. Reduce heat and bring to a simmer. Simmer, stirring occasionally, until thickened and a deep golden brown, about 2½ to 3 hours.
3. The mixture will thicken more as it cools. Use a wire whisk if needed to smooth out the mixture. Store in the refrigerator for up to 2 weeks. If necessary, loosen the refrigerated dulce de leche in the microwave using 15-second bursts.