Build a plywood box that matches the neighboring cabinets. Leave enough room for matching ceiling trim. Either put a backer only as deep as your deepest cookbook and block off the back, OR build a false back with hidden cabinet doors for seasonal things you can only reach with a ladder. I’d probably block it off because we’d just lose things back there.

My mom’s side were mostly newer immigrants in the Midwest. For the lines I can trace on my dad’s side, most did not. The three that fought in the civil war did not. A couple had 1-3. My paternal line vanishes before my GG grandfather, but my dad recorded the town gossip about him in the 1970’s. He was reportedly the result of an illegal relationship between an ex slave (mixed race, but the photos looked exactly like my dad) and my GGG grandmother. Who was reportedly disowned and changed her last name to my maiden name. There was a lot of drama, and likely a genetic defect because they all died young and started a long line of people dying in their 30’s from heart attacks until modern medicine extended that to their 50’s with my grandfather. At any rate, that side of the family has a lot of “Indian Princesses” in the family tree. Mostly Creek, Seminole, or Cherokee. As the tribes in the Southeast fully accepted runaway slaves into the tribes for 300 years, I have only the one known mixed ancestor, but twice as much African DNA as Native American on 23&me. Interestingly, DH and I have one black ancestor thought to be from the late 1500’s in NC in common. Which is so far back it’s shocking it could be identified. I think DH’s family didn’t live in slave states but also managed to avoid the civil war as far as I can tell.