Line an 8-in. square pan with foil and grease the foil with 1 teaspoon butter; set aside., In a large saucepan, combine the sugar, milk, salt and remaining 2 tablespoons butter; cook and stir over medium heat until mixture comes to a boil. Boil for 5 minutes, stirring constantly. , Remove from heat; add the marshmallows, chips, nuts and maple flavoring. Stir until marshmallows and chips are melted. Spoon into prepared pan. Let stand until set., Using foil, lift fudge out of pan. Discard foil; cut fudge into 1-in squares. Store in an airtight container at room temperature.