If you’re reporting on a recipe where you are the first to report on it, reply to the OP, but if someone else has reported on a recipe, reply to their post. The posts aren’t nested, but replies are all connected, so it helps make posts about the same recipe easy to follow.
These days, we have one thread for each book/website/author, so when COTM covers multiple books by a single author, they’re all on one thread.