I tried making that last Saturday to bring to a Christmas open house and it was an epic fail. My saltines floated to the top, my toffee mixture became crystalline in the pan during the cooking procedure, and my chocolate chips didn't become warm enough to melt and, instead of being glossy, smooth and luscious, it was lumpy, dull and unattractive. A similar recipe had been posted in earlier versions of this thread so I thought it would be OK. Turns out I'm one of five people in the universe who goof up that recipe.
Have checked a cooking chemistry book out of the digital library and will check back in with an answer if I find one. Apparently, you need a pastry brush and water to prevent crystals from seeding more crystals on the sides of the pan. Using the candy thermometer would have been better if you happen to know the temp optimal for making caramel or toffee.
