Line an 8-in. square pan with foil; grease foil with 1 teaspoon butter., Cube remaining butter. In a large saucepan, combine cubed butter, brown sugar and milk. Bring to a full boil over medium heat, stirring constantly. Cook 10 minutes, stirring frequently. Remove from heat., Stir in maple flavoring, vanilla and salt. Add confectioners' sugar; beat on medium speed 2 minutes or until smooth. Immediately spread into prepared pan. Cool completely., Using foil, lift fudge out of pan. Remove foil; cut into 1-in. squares. Store in an airtight container.