Warning: You must let the can cool completely before opening it or burns may occur.
Remove the label from the can of sweetened condensed milk and place it unopened on its side in a heavy saucepan.
Cover with water at least an inch above the can.
Bring to a boil using medium high heat, then reduce heat and simmer for 2 hours. Check the water level occasionally and add more if needed to keep the can covered.
Remove from heat, drain the water, and let the can cool completely. It is best to put it in the refrigerator overnight. Warning: If you do not wait until the can is cooled, you could have a hot explosion causing burns and injury. Please be patient.
Once cooled, open the can and enjoy a thick caramel sauce. To thin the sauce, add a small amount of milk and stir well.
You can cook more than one can at a time.
Recipe by The Gluten-Free Homemaker at http://glutenfreehomemaker.com/yummy-carmel-topping-recipe/