This is especially good with black walnutsgiving an old-fashioned flavor to the fudge. Combine sugar, corn syrup, and heavy cream and cook to 244 degrees F. 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.