Start by heating the butter in a 4 quart microwaveable bowl in the microwave on high for about 1 minute, or ’til melted.
Then add the sugar, salt and evaporated milk, mixing well. Heat on high for another 3 minutes, stir it up, and heat on high again for another 2 minutes, or ’til the mixture just starts to boil.
Mix it up again with a rubber spatula, making sure to scrape the bottom of the bowl. Microwave again for 3 more minutes, then stir and microwave for another 2 1/2 minutes. Let set for 2 more minutes, and then stir in the chocolate chips ’til melted.
Add the marshmallow creme, vanilla and chopped walnuts, mixing ’til well combined.
Pour the mixture into a greased 9×13 pan, and let cool at room temperature.
That’s it! Just like with stovetop fudge, cut into squares and serve.