Pour condensed milk into a square baking pan. Cover tightly with foil.
Place pan in a larger oven safe pan. Place pans in the oven with the rack pulled out slightly. Fill the outer pan with hot water so that it comes up halfway. This creates a water bath in which to cook the milk with even heat.
Bake for 45 minutes. Refill water if it goes below halfway.
Continue baking for another 45 minutes.
Remove pan from oven.
Carefully uncover pan and pour hot Dulce de Leche in a bowl. Cool, cover and store in refrigerator for up to 1 week.
Use Dulce de Leche in any of your favorite recipes that call for or a rich caramel-like sauce .