If using candy molds lightly spray with non stick spray or add a few drops of oil and coat them with your finger. If using a jelly roll or bread pan, line it with parchment paper or spray and wipe off excess.
Wipe off the excess with a paper towel.
Pour syrup into a large saucepan or pot. The syrup will bubble up and foam so make sure you have a large enough pan.
Bring it to a boil over medium heat.
Once it boils add the butter and stir until melted.
Test the temperature with a candy thermometer. The temperature should be about 240°F (soft-ball stage) 32-34 degrees F above the point water boils at your elevation. See below for a link to determine your elevation by zip code.
Remove it from the heat and allow it to cool for a couple minutes.
Then stir it vigorously with a wooden spoon until it losses it’s gloss, thickens, lightens in color and turns opaque.
Stop stirring. If it cools too much it will be difficult to pour or spoon into molds and it may harden in the pan.
Work quickly. Pour the mixture into molds, smooth them off with a flat spatula or the flat side of a knife. As the candy cools it will begin to hard and you may have to spoon it into the mold.
Notes
Pro tips
The tricky part is learning how much to stir and when to stop stirring. If you stir too much the mixture will harden in the pan. If you don’t stir enough, it may not harden at all. If it hardens, add about ½ cup of water and slowly reheat. Start the process over again.
Did you know that water boils at different temperatures at different elevations? You need to check the boiling point of water at your elevation. Just enter your zip code.
Once you quit stirring, work quickly to get the candy into the molds. It may help to have two people working on it. One to pour or spoon the mixture into molds and one to smooth out the bottoms of the candy.