Line a 9x13, straight-sided baking pan with parchment paper. Be sure to allow enough parchment paper to overhang the sides of the pan. This will make lifting the cooled fudge out of the pan easier for slicing.

In a 3-4 quart saucepan on medium heat, add the granulated sugar, margarine, and evaporated milk. Stir to combine and cook, while stirring constantly, for 5-8 minutes or until the mixture reaches a hard (or rolling) boil.

Cook the sugar mixture for exactly 5 minutes at the hard boil stage while stirring constantly. Remove from the heat.

Add the semi-sweet chocolate chips to the hot sugar mixture and stir until the chips have melted and the mixture is smooth.

Add the marshmallow cream and vanilla extract. Stir again until the fudge mixture is smooth and no marshmallow streaks remain. Stir in the chopped walnuts.

Pour the fantasy fudge into the prepared 9x13 pan and spread it into an even layer. A small offset spatula works great to smooth out the thick fudge mixture.

Allow the fantasy fudge to cool completely before removing it from the pan and slicing it into 1x1 inch square pieces.