This is the only answer that sort of makes sense so far. For a pie with a crust, it lets you see what the crust looks like below the filling line.

I’m not a baker. Just a guesser.

Except that the crust where the window is would bake completely differently from the parts of the crust that would be touching the stoneware.

It’s so big and ceramic, and the hole is just that one side, It’s a good idea but I think it would be impractical.

It was not supposed to be used, the hole is to hang it at the store.

Viewing hole for your miniature otter museum.

Don’t put your privates in it.

It’s an Icelandic Fairy house with the roof missing. The hole is a window, and you’re supposed to give them a south facing view for good fortune.

I know this one! It’s a bed pan!