I have made layer cakes up as sheet cakes before. Just use the recipe for the cake part "as is", and bake in one layer in a 9 X 13 inch pan, filling the pan with batter about 2/3 full, and checking if it is done, starting after about 35 minutes or so and repeating every five minutes until a toothpick inserted in the centre comes out clean.

A two layer cake will more than fill one 9 X 13, if you double the recipe from Food Network, you will probably get 3 sheet cakes, and that would be plenty to serve 30 people.

The only tricky part is the raspberry flavour. Since it is a sheet cake, you won't be able to use it as filling. And fresh raspberries would be hard to come by at the end of February, otherwise I would say use them as a garnish on top of the cake, which would be truly lovely.

If you can find some dried raspberries, you could incorporate them into the batter for the cake, without changing the balance of wet to dry very much, as you would only need a few.

Otherwise, I would say add some berries or jam to the cake batter itself. Or possibly a layer of jam that will go under the icing, if you think it will cover up nicely (because raspberry jam peeking thru the icing might be a bit uggerly.

Hope this was helpful,

Carolyn!