Nut tella or 'Nuh'tella. That's how they pronounce it in Italy. I know this because I had a sister who went to Italy and got nutella from there. Before that we always got it from 'The Hill' in St. Louis, where my aunt lives. (It's an Italian town) Eventually it started coming out in World Market. And then it spread to become popular to most all Americans and was sold at most grocery stores.
'New'tella is what I have heard some people say. Maybe it's the American English pronunciation?