Method 1: Boiling

1. Remove the paper labels from the cans. I suggest boiling no more than 2 cans at a time. The more cans in the water, the longer it will take to cook. 
2. Place the cans on their sides and cover them with at least two inches of water.  Bring the water to a boil over high heat, then turn it down to medium. Check frequently to make sure the water level stays at least 2 inches above the cans at all times, throughout the entire cooking process. Cook for 3 to 3 hours. The longer you cook, the darker and richer the flavor, and the thicker it will be. Sometimes I cook it for 2 hours and use it for a fruit dip or sauce over ice cream. My favorite is to cook it for 3 hours and use it for frosting on a yellow cake.
3. Once the caramel is cooked, use a pair of metal tongs or a spider to lift the cans out of the boiling water. Transfer them to a towel and dry them. Leave the cans unopened, and left to cool for at least 1 hour. Then refrigerate the cans for at least 2 hours. If you open hot cans they will explode and the Dulce de Leche will run down the sides and make a mess. 
4. Refrigerate opened dulce de leche for up to 2 weeks. Place unopened cans in a pantry for up to 2 months.

Method 2: Baking

1. Preheat an oven to 425 degrees.
2. Open the sweetened condensed milk and pour it into a shallow baking dish such as a pie dish. Cover the dish tightly with foil.
3. Place the dish in a roasting pan or any pan that’s at least 2 inches deep. Place the foil covered dish in the pan. Place the pan on the oven rack and pour boiling water around it until the water comes at least have way up the side of the baking dish. Make sure the foil is wrapped tightly around the edges of the baking dish to ensure no water gets through.
4. Bake for 1 hour & 45 minutes. Transfer to a cooling rack and remove the foil. Allow the dulce de leche to cool until it’s at least warm or cool. Whisk with a hand whisk to get rid of any lumps and make extra smooth.
5. Transfer to a sealed container and refrigerate for up to 2 weeks.

Method 3: Cooking opened on a stove.

Martha’s way