Line a 9x5-in. loaf pan with foil and grease the foil with 1 teaspoon butter; set aside. Butter the sides of a small heavy saucepan with 1 teaspoon butter; add the sugar, cream, corn syrup and ginger. Bring to a boil over medium heat, stirring constantly. Reduce heat; cook until a candy thermometer reads 238° (soft-ball stage), stirring occasionally.
Remove from the heat. Add maple flavoring and remaining butter (do not stir). Cool to 110° without stirring, about 1 hour. With a portable mixer, beat on low speed for 1-2 minutes or until fudge begins to thicken. With a clean dry wooden spoon, stir in walnuts until fudge begins to lose its gloss, about 5 minutes.
Spread into prepared pan. Refrigerate until firm, about 30 minutes. Using foil, lift fudge out of pan. Discard foil; cut fudge into 1-in. squares. Store in an airtight container in the refrigerator.