Melt the sugar, butter, corn syrup, and salt together in a large, heavy-bottomed sauce pan over medium heat.
Once the mixture comes to a boil, add the evaporated milk a little at a time, taking 15 minutes per can and stirring constantly. A labor of love indeed.
Once all the milk is added use a candy thermometer and bring the mixture to 238F and not a touch hotter! Even 2 degrees hotter will make them chewy instead of soft.
Pour into a parchment lined 13x9 pan and cool completely. Cut and serve. Enjoy!