This is especially good with black walnutsgiving an old-fashioned flavor to the fudge. Combine sugar, corn syrup, and heavy cream and cook to 120ºC . Remove from heat and add semisweet chocolate, marshmallow, Fondant, and vanilla. Beat by hand or in a mixer until thick and creamy. Add walnuts. Spread in a 9x13-inch pan. Cut into squares when mixture holds its shape. Makes about 80 pieces.