Made this last night...
I'm not sure about the kettle caramelisation procedure yet; need to do a little research into what develops the deeper caramel flavours (think dried fruits - raisins etc). I boiled down from a gallon to a pint, ended up with something that looked and tasted like LME with a few slight caramel tones. I did notice that it was anything but homogenous, so it may be that the deeper flavours were hiding in the more lumpy bits that seemed to form (crystals, I think). I would have continued to boil but I was rather concerned that the stuff was going to burn, so avoided that. I think perhaps I need to separate the concerns: boil down to a couple of pints, then add the lid to boil it for longer without boil-off, then take it off again to finish boiling down. Research needed.
Threw the whole thing on the 1728 yeast cake and it's happily bubbling away this morning.