Preheat oven to 350°F.

In a medium saucepan, heat sugar over medium heat, stirring constantly until it melts and becomes a golden-brown caramel. Quickly pour the caramel into a 9-inch round baking dish, tilting to coat the bottom evenly.

In a large mixing bowl, whisk together eggs, sweetened condensed milk, evaporated milk, and vanilla extract until smooth.

Pour the custard mixture over the caramel in the baking dish.

Place the baking dish in a larger roasting pan and fill the roasting pan with hot water to about halfway up the sides of the baking dish.

Bake for 60 minutes or until the custard is just set and a knife inserted into the center comes out clean.

Remove from oven and water bath, then cool to room temperature. Cover and refrigerate for at least 3 hours or overnight.

To serve, run a knife around the edge of the flan to loosen it from the dish. Place a large plate over the baking dish and invert the flan onto the plate. The caramel sauce will flow over the flan.