I had a similar issue, and after a couple of experimental runs, used a sheet pan, but I needed to place something heavy on top of that. I used a brick, and it worked fine. The rising power of dough pressing uniformly on the entire surface of the lid is considerable, and, even when the rise during the bake is just an eighth of an inch (or less) above the bottom pan's edge, it can lift a sheet pan and moisture will escape.

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