Now, the poncy among us will say it's 'Mo-ette' as the French do say "Mo-ette ay Chandon" (phonetic-ish spelling), but the poncy are WRONG.
They're wrong, as are the bleedin adverts on this one, because the 't' is only pronounced because the 'et' follows. The 't' is effectively inserted to make the words work 'in the mouth'.
So, if you are not saying the 'et Chandon' bit, you should just say 'Mo-eh' or 'Mo-ay' (anglicised version).
At least, that's what my French training suggests......
Pedants, please contribute.