Toast nuts by spreading on a baking sheet and baking at 375*F for 5-7 minutes. Set aside.
Spread mini marshmallows onto a baking sheet an place in freezer while fudge is being prepared.
Prepare a 9"x13" pan by lining with parchment paper, allowing the paper to hang over the edges a bit, so you can use that to pull the fudge out of the pan later.
In a large pot (I used my Le Creuset French Oven), combine sugar, butter and evaporated milk. Heat over medium-high heat until it reaches a boil, then reduce the heat a bit and simmer, while stirring almost constantly, until mixture registers 234*F. This may take 10-15 minutes, or more. (If you do not have a candy thermometer, once at a full boil, continue boiling for 5 minutes, stirring continuously.)
As soon as the mixture reaches 234*F. remove pan from the heat and stir in nuts (reserve a few for the top of the fudge, if desired), marshmallow fluff, vanilla and salt. Stir, to fully incorporate marshmallow fluff, and allow mixture to slowly cool.
When the mixture has cooled to 160*F (this may take 15 minutes or more), add chocolate, covering fully with warm mixture to help the chocolate melt. Allow the chocolate to melt on it's own a few minutes, then stir until chocolate is fully melted and well combined.
When the chocolate has been fully incorporated, add frozen marshmallows and stir to even distribute. Reserve a few for topping the fudge, if desired.
Spread fudge into prepared pan, and spread with spatula as best as possible. Top with a piece of plastic wrap, then use your hands to level out as smooth as possible. Remove plastic wrap and cool fudge in the refrigerator at least 4 hours.
To cut fudge, lift up on parchment paper overhang, and move to a cutting board. Use a sharp knife to cut into small squares. As needed, run the knife in warm water, then wipe dry between cuts.
Fudge may be store in an airtight container in the fridge for up to a month. Fudge is best when served at room temperature.