Add the sugar and water to a 20 cm / 8-inch metal cake pan or quesillera mold set over medium heat on the stovetop.

Let it melt undisturbed for 3 to 4 minutes, then swirl the pan gently, don't stir, until the sugar turns a deep amber color, about 8 to 10 minutes total. Watch closely in the last minute, it can jump from amber to burnt in seconds.

Remove the pan from heat immediately and tilt it to coat the bottom and partway up the sides with caramel. Set aside to harden while you make the custard.

Heat the oven to 175 C / 350 F and bring a kettle of water to a boil for the water bath.

Crack the eggs into a blender or large mixing bowl. Add the condensed milk, evaporated milk, vanilla and salt. Blend or whisk until smooth, about 30 seconds, without over-beating since too much air creates holes once baked.

Pour the mixture through a fine-mesh sieve into the caramel-lined mold to catch any foam or bits of egg white.

Set the mold inside a 33 x 23 cm / 13 x 9-inch roasting pan. Pour boiling water into the roasting pan until it reaches halfway up the sides of the mold.

Cover the mold loosely with foil and bake for 50 to 60 minutes, until the edges are set but the center still jiggles slightly. An instant-read thermometer inserted in the center should read 170 F / 77 C.

Lift the mold out of the water bath and let it cool to room temperature on the counter, about 1 hour.

Cover and refrigerate at least 4 hours, ideally overnight, until fully chilled and firm.

Run a thin knife around the edge of the mold, set a rimmed serving plate on top, and invert quickly. The caramel sauce will pool around the quesillo. Slice and serve chilled.