Prepare the 13 x 9-inch pan by laying down a sheet of aluminum foil followed by a sheet of parchment paper. Lightly coat the parchment paper with cooking spray.
In a large saucepan, whisk together evaporated milk and sugar. Bring to a boil over medium heat and add the candy thermometer. Allow the mix to reach 243 degrees Fahrenheit, stirring regularly for approximately 10-20 minutes.
While the sugar and evaporated milk is cooling, add the butter and chocolate to a separate bowl.
Pour the hot mixture over the chocolate and butter. If the evaporated milk and sugar do not appear to be smooth use a strainer while pouring it to remove any lumps. Whisk immediately after pouring with egg whisk.
Add the vanilla to the mixture and whisk until fully combined.
If your fudge mix appears grainy or not smooth, add in half and half. Add in one tablespoon at a time until the fudge is smooth and shiny.
If you desire, add the pecans to the fudge.
Using a spatula, pour the fudge into the pan. Use the spatula to evenly spread out the fudge.
Place the fudge in the fridge uncovered until it is fully cooled and set.
Once the fudge is set, cover with plastic wrap and return it to the fridge for three hours.
After the fudge has been in the fridge for at least three hours, flip the fudge over onto a cutting board and remove parchment paper. Dip a sharp knife into hot water, then trim the edges of the fudge and cut into squares.
Fudge makes great presents for the holidays to give your friends and family.