Preheat the oven to 350°
Melt the cup sugar in a medium saucepan over medium heat, stirring frequently, until it turns into a dark caramel amber color, 9 to 10 minutes. Carefully pour the amber colored caramel into the flanera.
In a mixing bowl, combine the condensed milk, evaporated milk, whole eggs, egg yolks, salt and vanilla. Whisk to combine.
Place the flanera in a 9x13 baking dish. Using a strainer, pour the flan mixture into your prepared flanera. Fill the baking dish with warm water halfway up the sides to create a water bath/baño Maria. Cover the flan with the lid of the flanera or with aluminum foil.
Bake the flan for 1 hour or until the centers jiggle slightly when shaken. Let the flanera cool in the water bath, then refrigerate for at least 2 hours.
30 minutes into baking, add in more water to the water bath. You do not want your water bath to boil, if that boils your custard will boil and no one wants flan with bubbles in it. To maintain a creamy consistency, be sure to add more water so it won't boil.
When ready to serve, run a paring knife around the edge of the ramekin, place a serving platter or large plate over the top, and invert the ramekin, Give the flan mold a few taps with a spoon to help release the flan from the mold. Liquid caramel will drip down the sides of the flan.