Line a 9x13 inch baking pan with foil. Butter the foil with about 1 tablespoon butter; set aside. In a very large heat-proof bowl, combine the Hershey bars, chocolate chips, marshmallow creme and vanilla.

In a large heavy saucepan over medium-low heat, combine the evaporated milk, sugar and 1/2 cup butter. Bring to a boil, stirring constantly. Boil and stir for 4 1/2 minutes. Pour boiling milk and sugar mixture over chocolate mixture.

Stir vigorously for about 2 minutes until chocolate is melted and mixture is smooth and creamy. Stir in nuts, if using.

Pour chocolate mixture into prepared pan. Cover and refrigerate until firm. Using foil, lift fudge out of pan and cut into squares. Store in an airtight container in the refrigerator for up to 3 weeks, or freeze for up to 3 months. Fudge tastes best if brought to room temperature before serving.