http://www.accio-quote.org/article....i-3.htm

Это недалеко от начала 3-й части, но если не найдёте, вот скопированный кусок:

MA: What about Harry's family — his grandparents — were they killed?

JKR: No. This takes us into more mundane territory. As a writer, it was more interesting, plot-wise, if Harry was completely alone. So I rather ruthlessly disposed of his entire family apart from Aunt Petunia. I mean, James and Lily are massively important to the plot, of course, but the grandparents? No. And, because I do like my backstory: Petunia and Lily's parents, normal Muggle death. James's parents were elderly, were getting on a little when he was born, which explains the only child, very pampered, had-him-late-in-life-so-he's-an-extra-treasure, as often happens, I think. They were old in wizarding terms, and they died. They succumbed to a wizarding illness. That's as far as it goes. There's nothing serious or sinister about those deaths. I just needed them out of the way so I killed them.

Наверное можно наложить на бутылку (или блюдо в данном случае) постоянно действующее заклинание такого рода, чтобы она сама перенаполнялась до тех пор, пока есть вино (или бутерброды) там, откуда оно (или они) появляется . И вообще, Гермиона говорила, что можно увеличить количество еды, если она у тебя уже есть, это не противоречит закону Гампа .

ЗЫ: готовое оборотное зелье, я думаю, стоит отнюдь не пару галлеонов.