Line an 8-in. square pan with foil and grease the foil with butter; set aside. In a microwave-safe bowl, melt chips; stir until smooth. Stir in the milk, confectioners' sugar, amaretto and salt. Stir in 2/3 cup walnuts. Pour into prepared pan; sprinkle with remaining walnuts. Chill for 2 hours or until firm.
Using foil, lift fudge out of pan. Discard foil; cut fudge into 1-in. squares. Store in an airtight container in the refrigerator.