Butter a 9x13 pan and set aside.
Combine sugar, corn syrup and salt together in a deep, heavy bottomed pan. Cook on medium high heat, and stir frequently until mixture begins to boil. Place lid on top of pan and leave in place for 2 minutes. Remove lid and use a silicone spatula to scrape down the sides of the pan. Continue cooking until color starts to change to yellow. (This takes about 14-15 minutes when cooking at 8 on an induction burner, your time will vary)
Turn down heat to about a 6 (medium heat) and add cream mixture in a stream while stirring frequently. Continue to stir and increase heat up to a 7 (medium high heat). Put your candy thermometer in your pan.
Continue cooking while stirring frequently until medium or firm ball. (232° Fahrenheit, or 222° in high altitude)
Turn off the heat and stir in your vanilla. Then if desired stir in your nuts.
Pour into your prepared pan and let rest, covered in a cool place for at least 6 hours. Or overnight.
Cut and wrap in waxed paper, plastic wrap or parchment. Place in an airtight container.
Will keep 6-9 months if stored in an airtight container away from heat and light.