Step 1

Line an 8x8 baking dish with parchment paper, be sure the paper goes up along the sides of the baking dish with a bit of overhang.

Step 2

Add the butter to a 4 to 5-quart heavy-bottomed saucepan over medium heat. (Attach a candy thermometer to the side of the saucepan to keep a more accurate temperature reading.) Allow the butter to melt, then add the evaporated milk and granulated sugar. Stir constantly, even after the sugar melts, until the thermometer reaches 235°F (the softball stage). Remove the saucepan from the heat.

Step 3

Quickly stir in the chocolate chips. Once the chocolate chips have melted, add the vanilla and the marshmallow fluff. Keep stirring until the marshmallow fluff is completely incorporated. Stir in the chopped walnuts.

Step 4

Carefully pour the fudge into the prepared baking dish. Tap the sides of the baking dish to release any bubbles. Allow the fudge to rest for 30 minutes. Chill the fudge in the refrigerator for at least 3 hours before slicing 6 rows x 6 rows. Keep refrigerated until ready to serve.