Combine the chocolate and marshmallow creme in a large bowl; set aside.
Combine the sugar, butter, milk and salt in a heavy skillet. Bring to a rapid boil, then boil 6 minutes, stirring constantly. Remove from heat and stir in the vanilla.
Pour the hot butter mixture over the chocolate mixture in the large bowl. Stir with a wooden spoon until smooth. Add the nuts and mix well.
Spread the fudge into the prepared pan. When cooled, cut into 1-inch squares.