Most of the "make RPi Linux boot fast" guides out there use the same approach: Start with a tiny Debian and remove stuff until it's faster.

There's not a lot of good information about attacking it from the other way: Start with a bootloader, firmware, and a kernel, and add only the stuff that you need. I mean, it's probably out there on the web somewhere, but I've found it tough to find among all the "just strip down Debian" blog posts. If anyone has experience doing this and could point me to a few resources, I'd be grateful!