Bring mixture to boil - let come to rolling boil and boil at least 6-8 minutes. shut off heat. Add the marshmallow fluff and chocolate chips. Add the Tablespoon of vanilla. Stir mixture and then beat for a couple of minutes. Add another 3 Tablespoons of butter and stir until melted. Pour into buttered 9x13 pan. You can add a the cup of walnut or pecans if you like. Aunt Delores used to use 2 8 inch square pans and pour half of mixture in one pan and add a cup or so of walnuts or pecans to rest of mixture and pour into other buttered pan. This way you can have with and without nuts.