To prepare Puerto Rican flan, add 6 large eggs to an electric mixer, and beat the eggs until they are the consistency of a light custard. Add 1 cup of sugar, 1 14-ounce can of sweetened condensed milk, 2 13-ounce cans of evaporated milk and 1 tablespoon of vanilla extract. Blend the ingredients just until the mixture is smooth.
For the light caramel that typically covers flan, combine 1 cup of sugar and about 1/4 cup of water in a Pyrex measuring cup. Microwave for five minutes, or until the simple caramel takes on a golden color. Microwave for an additional 30 seconds as required until you achieve the desired color.
Pour the caramel into a non-reactive flan pan, and swirl it around to completely cover the bottom of the pan. Allow the caramel to cool and set before adding the custard. A flan pan is very similar to a tart pan or a deep dish pie pan, and these pans make great substitutes. Special Bundt pans with a lid and a double boiler are also available.
Preheat the oven to 350 degrees Fahrenheit. To cook the flan in a flan pan, prepare a bain Marie. Bring a kettle or saucepan of water to a light boil, and set aside. Place the flan pan with the custard in it into a large roasting pan first, then carefully pour the simmering water into the roasting pan until it is 1 to 1 1/2 inches deep.
Bake for 60 to 90 minutes, until a knife inserted in the center of the flan comes out fairly clean. Chill and serve.