I have made toffee for the past 43 years and am a home economist. The trick to not having your candy chrystalize is to not disturb the sugar crystals in solution. It's a supersaturated sugar solution and you need to make sure you don't drop any sugar crystals from the side of your pan when pouring out your mixture. You can take a piece of cheesecloth and wrap it arount the tines of a fork and dappen it. Run it carefully around the sides of your pan before you pour out your mixture and turn off the heat. When you pour out your mixture DON'T scrape the sides. After it's cooling just let it sit and don't agitate it. Just let it cool undisturbed and then you can break it into pieces. You should prep with a thin film of butter or butter pan spray.