white chocolate frosting

An 8 1/2 by 11 usually cuts 12 portions. A full sheet usually 75-90 at least I get that much

pastrycake,

Do you have "The Cake Bible"? RLBeranbaum? There's lots of info in her book on serving ratio to pan size.
I believe Rose HAS a white chocolate buttercream frosting in her book also. (I find white chocolate frosting persnickety and less stable than plain buttercream. It's low melting point has presented problems for me.)

Re: pan size....Do you mean a full commercial size sheet pan? 18" by 26" I feed around 60 people generously. (More if there are layers) You need a commercial oven to bake in these, and do consider the area of refrigeration necessary (no side by side!). Managing large heavy layers can be unwieldy.

9" x 11" is a standard size sheet pan. As stated, feeds 12.

Save yourself some grief...make cupcakes! Much easier to manage, store and frost..and they're so popular. You can make several varieties, including a vegan option and you'll be the hero. Two excellent cupcake books: Tack | Richardson's "Hello Cupcake" or Martha Stewart's "Cupcakes" and go to town! A good vegan cupcake cookbook is "Vegan Cupcakes Take Over the World".

I like to transport and give cupcakes in these:
Go to: plasticcontainercity.com (click on muffin and cupcake)
Scroll down to item: F2229-89

Dolores

Beranbaum's white chocolate cream cheese buttercream is wonderful and keeps very very well even in the heat. I used it in a wedding cake in 100 degree heat. The white chocolate helps keep it solid.