Umm... No, you can't. This particular Dark Knight encounter happens IMMEDIATELY after repairing Hanth's Forge, before Horace's shop (and therefore vegetables for the higher-end recipes) is even unlocked. This also means any plug/ring sets above the Don't Touch My Set are also unobtainable at this point.
EDIT: I didn't mean to sound disrespectful or anything at all with my reply. I really love this game and thank you for all the hard work you put into it.