In a medium saucepan, combine granulated sugar and a splash of water over medium heat. Stir gently until the mixture begins to melt, then stop stirring and let it cook until it turns a rich amber color, about 8-10 minutes. Carefully pour the hot caramel into a flan mold, swirling to coat the bottom, and then set aside to cool while you prepare the custard.

In a large mixing bowl, crack and whisk together the eggs until frothy. Gradually add the sweetened condensed milk, whole milk, and vanilla extract, mixing gently to combine everything into a smooth mixture.

Once your custard mixture is ready, pour it into the cooled caramel-coated pan. Cover the flan tightly with aluminum foil to trap steam, ensuring a gentle baking process.

Prepare a larger baking dish and place the flan pan inside. Fill the outer dish with warm water until it reaches halfway up the sides of the flan pan, creating a bain marie.

Preheat your oven to 350°F (175°C). Carefully transfer the bain marie setup into the oven and bake for approximately 1 hour and 15 minutes.

Once baked, remove the flan from the oven and let it cool at room temperature for about 30 minutes. Carefully take the flan out of the bain marie and refrigerate it for at least 4 hours, or ideally overnight.

When you're ready to serve, run a thin knife around the edges of the flan to loosen it. Invert it onto a serving plate, allowing the caramel to flow over the top and down the sides.