Preheat oven to 350 degrees F (175 degrees C). Prepare a hot water bath.

In a medium saucepan over medium-low heat, melt sugar until liquefied and golden in color. Carefully pour hot syrup into a 9-inch round deep glass pie plate, turning the dish to evenly coat the bottom and sides. 

Place the pan with the custard into a larger baking pan and pour enough hot water to go about halfway up the sides of the pan with the caramel sauce.

Place the eggs, condensed milk, evaporated milk, and vanilla in the bowl of the blender and blend until smooth. Pour the egg mixture into the baking dish over the caramel sauce. Cover with aluminum foil.

Bake in preheated oven for 1 hour and 15 minutes. 

Carefully remove the roasting pan from the oven and then remove the flan dish from the water bath. Remove the aluminum foil and let the flan cool completely at room temperature. After the flan is cool, refrigerate it for at least 4 hours (overnight is better!). 

To serve, carefully loosen the flan from the edges of the pan with a knife and then invert it on a serving plate.