Bride wanted to serve sheet cakes. So I baked one large square cake, cut the center out and filled with dummy styrofoam. Did same with the cut-out piece to make the second layer. So bottom two layers are styrofoam surrounded by cake. Top two tiers are cake. Styrofoam centers helped square up the cake and keep it level. It was lighter to transport. Bride and groom didn't have to worry about which layer to cut from in the ceremony. The caterers could easily cut two inch slices from around each of the bottom tiers without dis-assembling the cake. Worked great.