I've just checked my Concise Oxford English Dictionary - apparently it can be pronounced either way - 'nu:ga: (ie noo gar) or nugget (I can't type the special characters for that one lol).
The COED says it's 19c from the French (Provencal)
nogat, from
noga 'nut'.
A website I found (
http://www.flakmag.com/misc/nougat.html) states that
the word itself is French, with an assumed derivation from the Vulgar Latin "nuca," which relates back to the origin of the word "nuts."
Interestingly enough (ok, maybe not !) when I checked the derivation of the word
nut in the COED, it said it was from the Old English
hnutu of Germanic origin......