Looking through my IT cupboard recently I came across an opened (but almost full) box of Thornton's "Special Toffee (Original)" which I had moved from my desk to stop the cat from eating too much of it. Sadly, with a BB date of December 2019, and stored under distinctly sub-optimal conditions, and while continuing to look in perfect condition, the mouth-feel was now one of fudge rather than of toffee ...
With nothing to lose (I hate fudge), I researched how toffee was made, found that the optimal temperature was of the order of 150C, and set out to re-make the toffee using my halogen oven. The toffee was in two main chunks, so I melted the first (in a clean Fray Bentos steak-and-kidney pie tin from a few nights ago), and once it was molten put the larger chunk on the top. When it had all melted down I gave it a good stir, test-dropped a spoonful into cold water, then poured off the excess butter that had come out during the re-making process and left it to cool. When I judged that it was firm enough to remove from the tin, I prised it out, put it in a plastic bag, and transferred it to the freezer.
I am delighted to report that it is now once again absolutely perfect toffee, and (in my opinion) even better than the original because it is now further caramelized.
** Phil.