I'm wondering if anyone knows the origins of why the one who makes the bracha on challah on Shabbat takes a piece for himself first. I'm most curious if this actually shows up in sources, or if it's a custom (or both, obviously). Thank you!
This is indeed the correct practice. Whenever one person is saying the blessing for everyone present at a more formal meal, and is providing each of them with a piece from his loaf, they should not eat before he does.
(Note that according to some opinions there is no problem if he passes them their pieces before he eats, but they should not start eating before he does. According to others he should not even pass them their pieces before he eats.)