That is a good looking burger. I had some scrap 5.5" id x 6" od DOM laying around so I cut a few of these 3/8" long.
They are carbon steel which I think should be ok if it's seasoned like cast iron would be. I plan on welding it inside and out like the left side of the drawing, the right side is welded only on the outside but I don't like the seam left on the inside where bacteria can hide.
I see Meyer Metal Works is gonna hook you up but if I get these done in the next 2 weeks let me know if you would like one.