A parchment lid is a handy thing to know how to make. Once you know the technique you can also make parchment rounds to line layer cake pans. Thomas Keller likes to use them for covering braises and simmering soups in his cookbook Ad Hoc.
If you have Ad Hoc, go get your copy and check the directions for making a parchment lid on page 120. My edition has an error which I discovered while making the beef stroganoff. The directions start by telling you to fold a large rectangular piece of parchment paper in half to give you a square bigger than the pot to be covered. In the margin of your book make a note to fold the square in half again. Then continue on with the rest of the instructions.
That way you’ll have the correct instructions when you need them, and you won’t be in a frazzle because you’re wondering why you followed the directions exactly and ended up with half a lid instead of a full circle.
I did confirm the error with Michael Ruhlman and he thought it had now been caught. So maybe later printings won’t contain the error.
And if you don’t have Ad Hoc, but would like to know how to make parchment rounds, here are directions at The Kitchn.