In a saucepan over medium heat, combine sugar and water. Let it melt and bubble without stirring, just gently swirling the pan occasionally. Once it turns a deep amber color, quickly pour into a 9-inch round cake pan. Tilt to coat the bottom evenly. Set aside.

In a blender, combine condensed milk, evaporated milk, eggs, vanilla, and salt. Blend until smooth. Let it sit for a few minutes to reduce bubbles.

Pour the custard over the caramel. Place the cake pan in a larger baking dish and fill the outer dish with hot water halfway up the sides.

Bake at 325°F (163°C) for 50-60 minutes, or until just set but still slightly jiggly in the center.

Remove from the oven, let cool to room temp, then refrigerate for at least 4 hours or overnight.

To unmold, run a knife around the edge and invert onto a plate. Give it a gentle wiggle.