High altitude toffee

I had the same problem at low altitude. Frustrating! A waste of time and butter! I've also made toffee successfully for many years. I was cooking on an induction range with using an all clad pan. I cooked it again using a small lecreuset cast iron pot and it worked.

Thanks very much for your suggestions. I guess that after 40 years of baking I'm going to have to relearn some skills to compensate for the altitude change between California and Utah.

I don't have high altitude situation, but this blog explains it.
http://userealbutter.com/2007/09/04/almond-toffee-recipe/

Well, now that you're living at 4500 feet, I'd suggest that now is the time to get out your thermometer. It will lend you more consistent results than eyeballing it. Where do you live, by the way?

Yes, it crystallized but not until it had been boiling quite a while. It just never got brown like it's supposed to; I've never used a thermometer when making this, I just eyeball it and take it off when it gets to be the right color, but that never happened today. Weird.

It sounds as though it crystallized, which doesn't necessarily have anything to do with altitude. To prevent crystallization, you can either place a tight-fitting lid on your pot until after the mixture comes to a boil, which causes steam to build up and effectively wash down the sides of the pot, or you can carefully wash down the sides with a brush and water, but only until a boil is reached. The principal difference that you will notice with altitude is that your toffee will take a bit longer to reach temperature because water boils a 1 degree lower for every 500 feet of elevation beginning at 1000 feet.