Combine granulated sugar and water in a small saucepan over medium heat. Stir until sugar dissolves, then cook without stirring until it turns golden brown, about 8-10 minutes. Pour caramel into a 7-inch round pan, coating the bottom.

In a large mixing bowl, whisk the eggs gently. Add sweetened condensed milk, whole milk, and vanilla extract. Blend until just combined, ensuring a smooth texture.

Pour the custard mixture into the caramel-coated pan. Cover with aluminum foil and place in a larger baking dish filled with warm water, reaching halfway up the sides. Bake in a bain marie for even cooking.

Preheat your oven to 350°F (175°C). Bake for approximately 1 hour and 15 minutes until mostly set but with a slight jiggle.

Let the flan cool at room temperature for about 30 minutes, then refrigerate for at least 4 hours or overnight.

Run a knife around the edges to loosen the flan, invert onto a platter, and let the caramel flow over. Slice and serve chilled.