I’ve made a number of half sheet cakes but they have been quite thin- roulade cakes. For those you definitely don’t need a core.
For a 2” deep sheet cake pan, an inverted flower nail (and cake strips) might help the center bake a tad more quickly so that the edges don’t dry out waiting for the center to finish baking. You could also plan on syrup if you’re worried about it being dry. I’m sure with your experience and skill a sheet pan cake would be successful if you ever needed to make one.
Is the flower nail a better idea than a core?
Not sure if one is better than the other, but if I understand the process, the core gets filled with batter to make a sort of cake plug that you put back into the cake to fill the hole made by the core. That seems like a bigger flaw to cover up than a mark from a flower nail, and also like the little plug might get overbaked and not be as tender/moist as the rest of the cake.
You could always bake two 9x13 cakes and lay them together, side-by-side on a cardboard support to mimic a half sheet cake.
I agree with Julie on both points here. I havenít done a lot of large cakes, but the half sheet cakes Iíve done turned out well using an inverted flower nail and wrapping the pan with the cake strips. As far as using a plug instead of an inverted flower nail I donít know how different the results are since Iíve never done it myself, but from what Iíve read from others who have they do not like it nearly as well as using an inverted flower nail or the heat nails Ateco makes. And Julie is correct about using the plug. It gets filled with some batter and then placed in the pan and the cake bakes around the core. If you use one you have to grease and flower it the same as you would the cake pan before filling it with the batter. Then when the cake is done you remove the plug from the core and place in the hole formed from where the core was placed in the pan. And I also think this is a bigger flaw to cover up and deal with than a few tiny holes using some inverted flower nails or heat nails/cores.
Just as disclaimer, I do not own stock or work for Amazon or Ateco, but I have heard nothing but good things about Atecoís heat nail/core. From what Iíve read people who use them like them even better than the inverted flower nail because it was designed for this purpose. Theyíre perfectly flat and will not rust over time since they are made of stainless steel. Iíve read that over time using a flower nail for this purpose causes it to rust.
You can get these from a variety of different cake baking/decorating suppliers, but this was the first link I found for them:
Good luck and happy baking, CRenee.