Line a 9-inch x 9-inch square pan with parchment paper, being sure to let it hang over the edges a bit. (This will make it easier to remove the fudge later.) Set aside.
To a medium saucepan, add the sugar, butter, and evaporated milk. Cook over medium-low heat until boiling. Continue to boil for 5 minutes while stirring constantly. (see note)
Remove the pan from the heat and add the chocolate chips and marshmallow creme. Stir until completely combined. Then fold in the walnuts and vanilla.
Pour the fudge mixture into the prepared pan. Allow to cool for at least 1 hour before cutting into 36 squares (6x6 grid).
Notes
This recipe makes 3 pounds of fudge. You can prepare it in a 9x13 pan for thinner pieces. The instructions will be the same.
If the fudge is cooked too long, it will be grainy looking and crumble when you cut it. As soon as I start to see the little bubbles forming around the edge of the saucepan, I start the 5-minute timer.
Store leftovers in an airtight container at room temperature for up to 2 weeks, or wrap in plastic wrap and freeze in a storage container for up to 3 months.