Butter one 8 inch pan and set aside. In a saucepan mix brown sugar, evaporated milk and salt. Cook over low heat and stir until boiling. Boil for 3 minutes .. Remove from heat and stir in chocolate chips, peanut butter and vanilla. Mix until smooth. Pour fudge into pan. Refrigerate 4 hours or until firm. Cut into squares. Share with a friend! and enjoy.