Butter a 9 x 13 cake dish or line with parchment and set aside
In a large heat proof bowl add the bag of marshmallows, chocolate chips and vanilla and set aside. (Fresh marshmallows work best for this recipe)
In a large pot (6 qt) on medium heat, place the butter and evaporated milk. Stir with a wooden spatula or a heat resistant silicon spatula, while the butter is melting.
Add the 5 cups of sugar and continue to stir until the butter, sugar and milk comes to a rolling boil.
Once it is at a rolling boil, set a timer for 9 minutes and continue to stir.
If you prefer to use a candy thermometer, you are looking for the soft ball stage which is about 230 degrees. 9 minutes works nearly like a charm!
At the nine minute mark, pour the butter, sugar, milk mixture into the heat resistant bowl containing the marshmallows, chocolate chips and vanilla--and STIR!
Stir until the marshmallows and chocolate are incorporated and you don't mean to, but you giggle a little, because it smells heavenly! It might be 2-3 minutes of stirring, depending on those marshmallows! ;)
Pour the fudge into the prepared 9 x 13 pan and press it into the pan.
Cover the fudge and move to the refrigerator for the fudge to set.
Let the fudge set for 2 hours at least, and then it will be ready to slice into squares for gifts or small pieces for a party. Enjoy this chocolatey goodness!