I did write and publish a book about making sweets/candy at home some decades back
There are currently at least three novels in various states of completion.
One historical, one space opera and a couple fantasy.
The historical one is based on the slave uprising at the laurion silver mines in greece.
Fascinating period of history, all mixed up with the peleponnisian wars.
I did almost finish a small book on picking edible fungi, but I'm not great at finishing projects - much better at starting them
One of these days the books will get finished.
As far as a decent sized non-fiction book. I suppose these days it would be a sociological/anthropological study of the impact of technology on human soceity in the latter part of the 20th century and the beginning of the 21st.
Although I tend to find with a lot of such books, that you just spend your time going: 'well yeah' and 'obviously'. And such like comments.