1. Line 8- or 9-inch square pan with foil, extending foil over edges of pan.
2. Melt chocolate chips with sweetened condensed milk and salt in heavy saucepan over low heat. Remove from heat; stir in nuts, if desired, and vanilla. Spread evenly in prepared pan.
3. Refrigerate 2 hours or until firm. Use foil to lift fudge out of pan; peel off foil. Cut into squares. Store covered in refrigerator. About 2 pounds.
CHOCOLATE PEANUT BUTTER CHIP GLAZED FUDGE: Proceed as above; stir in 2/3 cup REESE'S Peanut Butter Chips in place of nuts. Melt 1 cup REESE'S Peanut Butter Chips with 1/2 cup whipping cream; stir until thick and smooth. Spread over fudge.