I have a customer wanting a cake shaped in a cross for her daughter's christening. The cake will need to serve 50-60 people. I would assume I should start with a square cake and cut it into a cross shape. My question is how big of a square cake do you think I would need in order to get the servings after I cut it into the cross? Also, how would I explain how to cut the cake in order for her to get the proper serving number?