Use a can opener to poke 2 small holes in the top of can.
Fill a small pot with 4 inches of water. Place can in water, then add or remove water so that the top of the can sits 1/4-inch above the waterline. Bring water to a simmer and let simmer for 6 hours. Top off water occasionally so that it remains at the same basic level. Don't worry if a small amount of the can's contents bubble up and cloud the water during the simmering process.
Let can cool, then open and skim off top 1/4-inch of condensed milk. What remains below should be a thick creamy, delicious caramel sauce. Serve with fresh fruit such as bananas, berries, star fruit, etc.