Prepare the molds: Use two llanera molds or one 8-inch round cake pan (or a 9Ă—5-inch loaf pan). Set nearby on a heatproof surface.
Make the caramel: Combine the granulated sugar and water in a small saucepan over medium heat. Cook without stirring until the syrup turns deep amber, 6–8 minutes, swirling the pan gently if needed to even the color. Immediately divide the caramel between the molds or pour into the single pan, tilting to coat the bottoms evenly. Let cool until the caramel hardens.
Mix the custard: In a large bowl, gently whisk the egg yolks just to blend—avoid whipping in air. Stir in the sweetened condensed milk and evaporated milk until smooth. Add the vanilla extract and fine salt and stir to combine. Strain the mixture through a fine-mesh sieve into a pitcher or large measuring cup; skim any surface bubbles.
Fill: Pour the strained custard into the caramel-lined mold(s), leaving about 0.25 inch headspace. Cover tightly with foil to prevent water droplets from entering.
Steam (stovetop method): Set up a steamer with gently simmering water. Place the covered mold(s) in the steamer, ensuring water does not touch the foil. Steam until the custard is set at the edges with a slight wobble in the center and a thermometer reads 175–180°F in the middle, 25–35 minutes for llaneras or 35–45 minutes for a deeper single pan. Avoid vigorous boiling.
Bake (oven alternative): Heat the oven to 325°F. Place the covered mold(s) in a roasting pan and add hot water to reach halfway up the sides of the mold(s). Bake until just set with a slight central jiggle and 175–180°F internal, 45–55 minutes. Remove from the water bath.
Cool and chill: Transfer to a rack, uncover, and cool to room temperature, about 30 minutes. Cover and chill until fully set, at least 4 hours or overnight.
Unmold and serve: Run a thin knife around the edges. Invert a rimmed serving plate over the mold and flip to release. Lift off the mold, letting the caramel sauce flow over the flan. Slice and serve well chilled.