Using a cold stick of butter, grease a large piece of parchment paper and then line an 8x8 square baking pan. Set aside.
Place the remaining 1 tablespoon of butter in a large glass or metal mixing bowl. Set that mixing bowl on a cooling rack. The mixture will be super hot and you won’t want to touch the moping bowl after you transfer the mixture. The cooling rack allows air to circulate all the way around the bowl, cooling faster.
Add heavy cream, sugar, light corn syrup, white chocolate and salt into a medium heavy saucepan.
Cook over medium-low heat, stirring constantly, until sugar has dissolved, approximately 10 minutes.
Increase to medium heat, bringing to a low boil. Do not stir or mix any longer. Attach candy thermometer and continue to cook without stirring. Allow candy thermometer to come to 240 degrees (soft ball stagand continue to cook for 1 minute. This can take 10-15 minutes, so be patient.
Carefully pour mixture into mixing bowl with butter. Do not scrape the bottom of the pan in case any of the sugar scaled to the bottom.
Whisk butter and pure vanilla extract into the mixture. It will be bubbly and hot. Be careful!
Allow to cool at room temperature for 30-40 minutes before mixing well and then transferring to the prepared and lined square dish.
Use a small offset spatula to quickly spread fudge to sides of pan and smooth top. Allow to further cool before covering and chilling in the refrigerator for at least 8 hours.
Lift parchment out of the square dish and cut into 1-inch pieces.
Store in an airtight container in the refrigerator.
If you’ve tried this recipe, come back and let us know how it was!