Line an 8-in. square pan with foil and grease the foil with butter; set aside.
In a heavy saucepan, combine the chocolate chips, milk and salt. Cook and stir over low heat until chips are melted. Remove from the heat; stir in nuts and vanilla. Pour into prepared pan. Chill for 2 hours or until firm.
Using foil, lift fudge out of pan. Gently peel off foil; cut fudge into 1-in. squares.