Line a square pan with enough parchment paper to cover the bottom and sides of the pan . Coat lightly with cooking spray and set aside.
In a medium saucepan over medium-low heat, using a wooden spoon, combine evaporated milk, brown sugar, corn syrup until sugar is dissolved.
Turn burner to medium-high heat and bring sugar mixture to a boil and cook until it just reaches the soft ball stage (230℉ on a candy thermometer)
Remove fudge mixture from heat and add butter-do not stir. Let cool until thermometer reads about 110 degrees.
Add walnuts to the butter and fudge mixture and beat fudge until it has just started to lose its shiny gloss..
Immediately pour fudge into a prepared pan lined with parchment paper. Use a loaf pan if you want thicker fudge. Cut cooled fudge into 24 equal pieces.
Video
Notes
Watch your fudge carefully at all times. To be successful you must pay attention to it while it is cooking and while you are beating it. If you do overbeat it, add a little bit of milk to the mixture to try and loosen it up some.The recipe card has Nanny's ingredients as written on her handwritten card. However I have adjusted the instructions to fit more modern times with the same results. This is why the instructions on the card do not say word for word what my Nanny's card says.