jim262 wrote:
The addition of baking soda may make it a relative of peanut brittle where 250º-260º hard ball stage is adequate for good texture and mouth feel of the finished candy.
Caramelizing sugar before adding other ingredients requires temperatures in the range of 340º and 360º depending on how aromatic one wants the finished product. A thermometer is not generally needed for this stage. Color and aroma are a much more reliable method of getting it right. Taking the sugar to these temperatures before adding the butter and nuts would make the flavor more like traditional English toffee that is cooked to the crazed crack head stage of 300º.
While I haven't done this, I would be afraid that the butter would burn (or at least some of it would) before the temp. would be brought down enough, plus it would be messy. This is probably why we never see this in toffee recipes. I have seen recipes that take the toffee up to 330º, but the 310º seems to create plenty of flavor, and the hotter it gets, the harder it is to spread thin, I have found. But then, there's only one way to test those ideas!
250-260º wouldn't really create much color or flavor, in my opinion. I know nut brittles are often a little lighter than toffee, but I like the darker versions.