Some recipes for toffee call for butter, some don't. I'd like to know please what adding butter does, and if I do add butter, will I still be able to make the stickjaw type toffee? Thanks in advance.
Butter largely acts to prevent the crystallization of sugar in toffee. This leaves the toffee smooth and breakable.
You should still be able to make stickjaw (or, if not authentic stickjaw, at least a more sticky) toffee. The consistency of toffee has more to do with the temperature you bring the toffee to while cooking. Here's a chart detailing the various stages of candy temperatures. For a sticky toffee you'd most likely want to bring your toffee to the soft-crack stage.
Here is a recipe for authentic, old-fashioned, stickjaw toffee but without butter.