How to Write a Nonfiction Book?

Imagine you're writing a nonfiction book. Would your system basically look the same as the one you've already outlined? I don't, yeah, I don't know that it would look all that different. One thing that comes to mind is I think the book would already be partially written. Not necessarily in prose form, but something that's happened to me again and again with essays I've written since I've adopted the system. Like at some point I'm going to write like a monograph about this thing. And when that happens, I will have much of the material at hand.