The Frog Commissary Carrot Cake seems to carry the title of World's Best Carrot Cake: https://athomebysteveposes.wordpress.com/2010/05/16/commissary-carrot-cake-recipe/ I found this out years ago right here on eGullet, of course. There's a thread about it floating around somewhere. I made it once for an occasion and everyone raved about it, that's for sure. It's not my personal favorite only because I prefer a plain old carrot loaf, and I still use the old Moosewood recipe for that (although I use AP flour rather than whole wheat). Congratulations to your father-in-law!
Not sure if this will work, but here's the link:
