1. Line a 9×9 baking dish with parchment paper and set aside.
2. Add sugar, butter, and evaporated milk to a large saucepan. Bring to a boil over medium heat, then turn down to a simmer.
3. Stirring constantly, let the mixture simmer for about 10-12 minutes, until the temperature reaches 235°F. Once the temperature is reached, remove from heat.
4. Add the chocolate chips to the saucepan and stir until they have completely melted. The mixture will be very thick.
5. Next, add in marshmallow fluff, vanilla, and salt, and mix to combine.
6. Add in walnuts and fold in using a rubber spatula.
7. Transfer the mixture into the bottom of the prepared baking dish and spread out evenly. You may top with additional walnuts if desired.
8. Let the fudge set for about 3-4 hours before serving.