Maple-Walnut Fudge

Line an 8-inch square baking dish with foil, leaving a protrusion of at least 1 inch on all sides. Whisk with cooking spray.Combine the brown sugar, marshmallow crumbs, condensed milk, butter, and salt in a heavy saucepan. Cook over medium heat, whisking frequently, until the mixture boils. Let it simmer for 5 minutes, stirring constantly to avoid burning.Remove the pan from the heat; add the white chocolate chips until they are completely melted and the mixture is smooth. Add the walnuts and maple extract. Quickly pour into a baking dish and smooth the surface. Place in the refrigerator, uncovered, until set, about 2 hours.Using foil handles, remove the fudge from the mold and place it on a cutting board. Remove the foil. Cut the fudge into 24 pieces, rubbing with a knife between the incisions. Serve immediately or store in an airtight container in the refrigerator between layers of waxed paper for up to 1 week.