Double the recipe for the Condensed milk. It should take about 2 hours of constant stirring to reduce down to 2 cups. For this recipe you only need 1 3/4 cups of the reduced milk, so you have to find something else fun to do with the 1/4 cup leftover. (try pouring "shots" of it and see how many you can do)
While the condensed milk is still hot, combine it with the chocolate chips over low heat. Stir until all of the chips are completely melted.
Take the mixture off of the heat and add the salt and vanilla extract. Mix in the nuts after that is all well stirred if you have them.
Pour into a wax paper lined pan that will allow the fudge to settle to 1/2 - 1 inch deep. Cool in the fridge for at least two hours before cutting it up.