Line 8" square baking pan with foil, extending foil over edges of pan. Combine sweetened condensed milk, baking chips, butter and salt in medium microwave safe bowl.
Microwave on HIGH 2 minutes or until melted and smooth when stirred.
Stir in 1 ¼ cups walnuts and maple extract until evenly blended. Pour into prepared pan. Sprinkle evenly with remaining ¼ cup walnuts (alternately, place walnut halves on top of where each square will be cut.)
Chill 1 hour or until set.
Remove fudge from pan by lifting edges of foil. Remove foil. Cut into small squares.