Preheat oven to 350 degrees. Place a baking pan filled halfway with water on bottom rack of oven. In a deep bowl beat eggs with a whisk; add condensed milk do not throw can away, instead, fill it with the Half n' Half or heavy whipping cream (using heavy whipping cream makes the flan richer), then add to eggs and condensed milk in the bowl. Add the vanilla and whisk or mix with electric mixer until blended well. In round cake pans (at least 2 inches deep, add Karo syrup to coat bottom of pan, then strain the egg mixture into the pan about three-fourths up to the top of pan. Carefully place filled pan in center of oven on top rack. Allow to bake for approximately 1 hour. Stick toothpick in center of flan, if comes out clean, it is cooked. Allow to cool and then refrigerate until fully cooled. Flip onto a plate that will accomodate the flan and syrup. (Straining the mixture, makes the texture creamier when flan is cooked.)