Solid book by Shriram Krishnamurthi that I actually used as the textbook when I taught undergraduate programming language theory. It’s a pretty concrete walkthrough which uses a Lisp to sidestep lots of syntactic stuff and get at the theory. I like it a lot.

Classic book by Benjamin Pierce that provides a really solid introduction to type theory as implemented in programming languages.

Probably the best defense of why C is still a compelling language today despite its flaws. I don’t agree with everything in it, but it’s the most cogent defense of C that I’ve seen, avoiding relying on vague claims of being “low level” or vaguely “simple.”