The best recipe for homemade toffee?

Technique is more important than recipe. There isn’t actually much variation in ingredients or proportions in toffee recipes. The hard thing about toffee is that two awful things are going to try to happen while you’re cooking it: the sugar is going to try to crystallize too aggressively and the butter is going to try to separate out. Keep these from happening, and you’ve got it made; if they happen, the texture of the toffee is crap.

The sugar does have to crystallize, but it needs to form extremely fine—invisible, actually—crystals, not “sandy” ones. Large crystals will try to form at the rim of the cooking mixture, where it’s coolest. Part of the answer is to use a very conductive cooking pot that will carry the heat up the walls of the pot to the rim. Heavy copper does this best. The preferred vessel is actually a round copper basin. Most household pots, especially steel or cast iron ones, don’t conduct heat well. The heat stays down at the bottom of the pot. Keep a little squeeze bottle of water handy. If you see crystals beginning to form at the rim (looks like wet sand), squirt a little water around the rim to help dissolve them. Also, cook the toffee on a high flame (electric stoves really don’t work well for toffee); the longer it takes to cook, the more problems you’ll have.

The butter separation issue is partly addressed by stirring like a beast through the last half of the cooking. Toffee contains so much butter that the sugar syrup is barely able to keep it in emulsion. If you’re lackadaisical in stirring, it will break out. Professional recipes partially get around this by adding soy lecithin, which helps keep the butter in line. You can get some at health food stores or Whole Foods. Add a teaspoon or so to your mix. It has virtually no flavor.

This recipe seems pretty fool-proof.

@thorninmud sounds pretty good :) very professional !