Start by greasing a 9x13-inch pan.

In a large saucepan, combine sugar, margarine, and evaporated milk. Heat over medium, stirring until the sugar dissolves.

Once the mixture reaches a full boil, continue cooking for 5 minutes, stirring constantly.

Remove from heat and stir in the chocolate chips until they're fully melted.

Add in the marshmallow cream and mix until well incorporated.

Finally, stir in the walnuts and vanilla extract.

Transfer the mixture to the prepared pan, spreading it evenly. Allow it to cool for at least an hour before cutting into squares.