Make the caramel: Cook the sugar and water over medium heat until the sugar melts and reaches a deep amber color.
Coat the pan: Immediately pour the caramel into the flan pan and carefully tilt the pan to coat the bottom.
Prepare the custard: Gently whisk together the condensed milk, evaporated milk, eggs, vanilla, and salt. Avoid incorporating excessive air.
Strain: Pour the custard through a fine-mesh strainer for a smoother texture.
Fill the pan: Pour the custard over the caramel.
Prepare the water bath: Place the flan pan inside a larger roasting pan and add hot water until it reaches about halfway up the sides of the flan pan.
Bake: Bake at 350°F (175°C) for about 50–65 minutes, until the edges are set and the center has a gentle wobble.
Chill: Remove from the water bath, cool, then refrigerate for at least 4 hours, preferably overnight.
Unmold: Run a thin knife around the edge, place a rimmed plate over the pan, and carefully invert the flan onto the plate.