Prepare a 13-by-9-inch baking pan with foil and a sheet parchment. Spray the parchment with a very light coat of oil
In a large sauce pot, fitted with a candy thermometer, whisk together the evaporated milk and sugar. Bring to a boil over medium heat and cook until the mixture reaches 234 degrees F. Stir occasionally and be sure to get the milk that is behind the thermometer. This may take between 10 to 20 minutes.
while the milk mixture is cooking place the chocolate and butter in a large bowl.
Pour the hot mixture over the chocolate and whisk right away with an egg whisk, which is more open and will not clog up with the thick fudge. (If the milk mixture looks as though it has any lumps in it then strain it over the top of the chocolate. If it looks smooth then don’t bother.) Whisk in the vanilla.
if your fudge looks as though it has seized (looks grainy, not smooth)…Add a tablespoon of the half-and-half and whisk in. Keep adding and whisking after each tablespoon of half-and-half until the fudge is smooth.In the end it should look shiny and smooth. (Add the nuts now if you want them throughout the fudge.)
Spread into the prepared pan using a spatula. Make sure it is spread evenly.Place it, uncovered, in the fridge until it is well cooled and set.Once it is set, cover with plastic and return to refrigerator for at least 3 hours.Flip the fudge over, remove the parchment, and invert onto a cutting board. Using a sharp knife dipped in a pitcher of hot water, you will trim the edges and then cut into squares. I cut mine into 6 strips on the short end and 6 strips on the long end to make 36 pieces.
Enjoy and be sure to have lots of help to eat these treats. They make wonderful gifts to your family, friends and neighbors.