Preheat oven to 350°F (175°C). Place a 9-inch round cake pan or bundt pan inside a larger roasting pan. Boil water in a kettle for the water bath.

Make the caramel: Heat 3/4 cup sugar in a heavy-bottomed saucepan over medium heat without stirring. As sugar begins to melt around the edges (about 4 minutes), gently swirl the pan to distribute heat evenly. Continue cooking until all sugar dissolves into a deep amber liquid, about 6-8 minutes total.

Immediately pour caramel into your cake pan, tilting quickly to coat the bottom evenly. Set aside to harden while you prepare the custard.

Blend the custard: In a large bowl, whisk eggs and remaining 1/4 cup sugar until smooth but not frothy. Add sweetened condensed milk, evaporated milk, whole milk, vanilla, and salt. Whisk gently until fully combined, avoiding excess air bubbles.

Strain the custard through a fine-mesh sieve directly into the caramel-lined pan to remove any egg solids and ensure silky texture.

Create the water bath: Place the flan pan inside the roasting pan. Carefully pour boiling water into the roasting pan until it reaches halfway up the sides of the flan pan.

Bake for 50-60 minutes until the edges are set but the center 2-inch circle still jiggles when gently shaken. The custard should register 175°F on an instant-read thermometer inserted in the center.

Remove from water bath and cool on a wire rack for 1 hour. Cover with plastic wrap and refrigerate for at least 4 hours or overnight.

To unmold, run a thin knife around the edges of the pan. Place your serving plate upside-down on top of the pan, then quickly flip both together. Lift the pan slowly, allowing caramel sauce to flow over the custard.