I've been making "English Toffee" for most of my marriage of nearly 50 years. I have used recipes with and without corn syrup. I find they are both delicious. I don't have the sugar crystal problem because I stir until the sugar is fully dissolved and simmering and then use a spatula to make sure the sides are clean. I also use a good nonstick sauce pan and really I have never had a problem with crystals. I now use 4 sticks of butter, 2 cups of sugar, 1/2 tsp. salt, and 1 tsp. vanilla and it's perfect every time. The secret is have the candy a dark amber so it will crack and not stick to one's teeth. I hate measuring corn syrup anyway! Good luck and Merry Christmas!

Another alternative to invert sugar is to add some cream of tartar. It breaks sucrose into glucose and fructose making crystallization less likely. I like to make caramels, and use a relatively small amount corn syrup with a bit of cream of tartar. Knock on wood, so far I've not had any problems with crystallization.

I run a small candy company and toffee is a regular product for me. I agree with the above that at least a small amount of invert sugar is necessary to make sure the toffee crystalizes properly. The most common is corn syrup, but I've also experimented with glucose syrup, brown rice syrup and golden syrup, all of which have worked fine for me. Like FantasticMrFox I also add a little bit of baking soda at the end of cooking to lighten the texture of the candy and keep it from being too hard and dense (I use just a 1/2 teaspoon for 2 pounds of candy).

I make a number of batches of toffee every year for the holidays and I agree with hardlikearmor and louie734 on the corn syrup. It really does make the process easier, especially when you're making it for the first time. Start out with the most basic butter, sugar, and corn syrup recipe to get used to the technique of toffee. You're pretty much guaranteed an easy success with that. If you continue to make it, use the same recipe a few times in a row and only then start branching out with different syrups or additions. With something that relies so heavily on technique, you really want to master that part before you start messing with the recipe. I've found that even the smallest details can affect my batches: moisture in the sugar or even air, type of pot, size of burner, the length of time I take to incorporate sugar into butter, etc.

Hi everyone, first post. Been making the same English toffee recipe since I was a kid. No corn syrup but I do wash down the sides of the pot with water and a pastry brush (especially in the beginning) to keep any sugar crystals from being reintroduced and causing the lot to seize. The only other help I might offer is to be sure to stir every once in a while, because like caramel, once it starts to scorch its difficult to control.

I'm not much of a candy maker, but the corn syrup is just chemistry. Doesn't have to be corn syrup, by the way, just some form of invert sugar. If you're specifically opposed to corn syrup, try asking at health food stores, they might carry a wheat based invert syrup, or try making your own:
http://www.cooks.com/rec/view/0,1823,147170-227206,00.html

I'm with hardlikearmor on the corn syrup... after making 7 batches of toffee (2 failed) over the last 2 christmases, I've had enough of sugar crystallizing and ruining my hard work. The corn syrup, added while the sugar's dissolving in the butter, is a safeguard against this 'seizing', which is not as dramatic as it sounds - until you realize that all your melting, temperature checking, and stirring have resulted in a greasy, separated batch of ruined candy. And the amount of corn syrup is really negligible, contributing to the chemistry of the candy-making, not the flavor profile or "healthfulness" (of something starting with a whole box of butter!).

I use a tablespoon of corn syrup in my pound of butter/2 cups of sugar recipe. Now I'm not saying that you'll definitely have crystallization problems without it, but I haven't had a crystallized batch since I started adding corn syrup.

As for which toffee would be better in cookies, I vote for non-seized, unruined toffee in my cookie! ...which sounds absolutely delicious, by the way.

You may also want to add some baking soda before pouring out the toffee. This will neutralize the acids in the sugar as well as create some aeration to lighten up the toffee and make it easier to chew.
If you skip the baking soda, you'll likely wind up with very (very) hard caramel.
Try it both ways (easy enough to do), but I'm pretty sure you want to go with the baking soda, especially if you are going to crack it and put it in cookies....assuming you care about not breaking teeth. :-)

The purpose of the corn syrup is to prevent the sugar from crystallizing. The butter should interfere with crystallizing making the corn syrup less necessary. Either recipe should work in cookies IMO, as long as the toffee comes out fine in the first place.