How much buttercream would you need to ice, and fill an 11x15 and put a border on top and bottom? I am making the decorations with fondant, so won't need extra for that.
thanks!

I use the better part of a triple batch of BC to do an 11 x 15 sheet cake.

At least three batches.

thanks! I hate running out of icing part way through.

This is the recipe my Wilton instructor gave me:

11X 15 CAKES

2 lbs Crisco
4 lbs Confectioners Sugar
1 cup either milk, water, lite cream
2-3 tsp flavor

Thanks GeminiKim. That seems like a lot of milk/water/cream. I will try it out.