Begin by lining a 9x13 inch baking pan with foil and lightly greasing it with butter. This will make removing the fudge easier.

In a heavy saucepan, combine the sugar, butter, and evaporated milk. Bring this mixture to a full rolling boil over medium heat, stirring constantly to prevent burning.

After boiling for 5 minutes, remove the saucepan from the heat. Stir in the chocolate chips until they are completely melted and the mixture is smooth.

Next, fold in the marshmallow cream, vanilla extract, and chopped walnuts (if using). Stir well until everything is thoroughly combined.

Pour the mixture into the prepared pan and spread it evenly. Let it cool at room temperature until set, which usually takes about 4 hours.

Once set, lift the fudge out of the pan using the foil and cut it into squares. Store in an airtight container.