I was in my LHBS a few weeks ago talking about this butterbeer recipe and the store owner and some customers overheard me. The owner shouts out "DIACETYL!!!" and they all start laughing.I'm late to this party, but just read the whole thread.
The buttery taste in Chardonnay is mostly from malolactic fermentation. The grapes' malic acid becomes lactic acid from ML Bacteria. Oak aging will lend vanilla flavors and perhaps contribute to this, but Chardonnays that don't undergo MLF have more of a green apple flavor.
That's as I understand it... I could be wrong.
I prefer red wine.
I WILL be making one of these concoctions when the 7th's movies come out on DVD. I'd prefer a brewed version rather than a mulled drink, but the cream soda based drink for the kids sounds great!