Baking Pan Prep: Take an 8" baking pan and butter it, then line it with parchment paper. You will want to make the parchment paper larger than the pan and let it hang over the edges by about 1 inch. Make sure to butter the parchment paper too.
Thermometer Prep: Don't skip this step!!!! You need to calibrate your candy thermometer. To do so, place it in a jar of boiling water, it should read 212 degrees Fahrenheit. If it doesn't adjust all the recipe temperatures accordingly.
Mixing Bowl Prep: Place a large bowl over a wire rack and place the tablespoon of butter in it. Keep it close by but out of the way.
Additional Prep: You will want to have a pastry brush handy
Directions
In a large heavy saucepan add the cream, sugar, corn syrup, and salt.
Turn on the stove to medium-low heat and stir constantly until the sugar is dissolved. It should take around 10 minutes.
Take your wet pastry brush and wash down the sides of the pan to prevent sugar crystals from forming.
Increase the stove to medium heat and bring the mixture to a boil. Continue washing down the sides while it boils.
Add the thermometer to the pan and let the mixture continue to cook, without stirring, until it reaches the soft-ball stage, 238 degrees Fahrenheit. Approximately 10 minutes but go by the thermometer, not time.
When it reaches this stage quickly pour the mixture into the bowl with the butter. It is very important you DON'T scrape the bottom of the pan.
Move the thermometer to the bowl and let the mixture sit, without stirring, until the thermometer registers 110 degrees Fahrenheit. Depending on temperature this can take anywhere from 1 1/2 hours to 2 1/2 hours. Patience!
At this point remove the thermometer and with a wooden spoon fold the mixture until it thickens, turns a lighter color and loses its sheen. It's about 15 minutes.
Pour the mixture into the square pan and spread it out evenly.
Place the fudge in the fridge for 8 - 12 hours, overnight is ideal.
Cut the fudge into 1-inch squares. Store in the refrigerator for up to a week.