Bring syrup to boil, do not stir, bring to 242 degrees F on medium heat. Watch this carefully as syrup may have a tendency to boil over. That is why the butter added; to prevent boil-over.
Remove from heat and allow syrup to cool to 205 degrees. The cooling can be expedited by placing pan in cold water.
Begin to stir by hand with a wooden spoon. When light colored streaks begin to appear it is time to pour hot mixture into rubber molds or 2 inch paddies on parchment paper.
The mixture may cool and sugar rapidly so you must not waste time here. You have about 3 minutes to pour the mixture into molds or on the parchment paper.
NOTE: If it doesn’t go well and it sugars too fast, put all sugar back into sauce pan, add 1 cup of syrup and start the process over. I have never had a problem getting rid of the “failed” sugar. See my contact information for molds and pouring funnels.