Before caramelizing the sugar in the pan you’re going to use for the flan, put the empty pan inside of the larger one that you’re going to use for the water bath then add water to the large pan to come at least one inch up the side of the pan that will hold the flan. Remove the pan that you’ll use for the flan.
For the flan, choose a 12-inch diameter pan with straight sides that can be heated on the stove and put in the oven.
Put enough water into a pan large enough to hold the pan with the flan so that the water comes one-inch up the sides of the pan with the flan.
Put the sugar into the pan selected for the flan.
Heat the pan with the sugar on medium heat until the sugar melts and turns dark brown. (A series of pictures follows showing the progression of the caramelization.)
Do not stir the sugar or caramel. Simply swirl the pan from time to time to mix the caramel. Rotate the pan on the heat occasionally to reduce hot-spots.
If the pan has a very heavy bottom, the retained heat will continue to brown the sugar off the heat. Stop caramelizing the sugar a little before you think it’s done otherwise it might burn. If it turns out that the caramel is not quite dark enough, you can heat the pan again briefly.
Remove the pan from the heat and allow it to cool during which time the caramelized sugar will harden on the bottom.
While the caramel is cooling, bring the water in the water bath to a simmer on the stovetop then put the pan into a 350°F oven.
Meanwhile, combine the condensed milk, evaporated milk, eggs, vanilla extract, and salt. Mix well.
When the caramel is hardened, pour the milk-egg mixture on top.
Cover the pan tightly, either with foil or with a lid.
Put the pan into the water bath in the 350°F oven.
Bake for 1 hour 15 minutes at 350°F.
A knife inserted in the center of the flan should come out clean. If not, cook a few minutes longer.
Remove the flan from the oven and cool to room temperature.
Refrigerate at least 8 hours. Overnight is best.
When ready to serve, run a knife around the edge of the flan.
Put a large platter upside down on top of the pan with the flan. Quickly flip the entire set-up over. The flan should come out of the pan in one piece. Pour any remaining caramel syrup onto the flan.