https://www.buildyourownlisp.com/
It's been in my bookmarks for a long time but I've never really had time to really start it. The "who is this for" page say:
"This book is for anyone wanting to learn C, or who has once wondered how to build their own programming language.".
Well, I'm fairly competent in C (but not great) but would like to get a glimpse of what it's like to build my own language. Is it worth the time?
If you want to build a programming language in general, I strongly recommend https://craftinginterpreters.com/
That said, it is not a good good way to learn neither how to write a Lisp nor how to use C the proper way. Some of the stuff is very idiosyncratic or even questionable.
Again, for me it was fine because also used other sources to complement it and it got me interested and thinking about various topics. Just beware that it teaches things that will hold you back if you ever became serious about implementing a Lisp that is more than a toy.
If you already quite OK with C and don't need much hand holding I would suggest going through MAL instead.
See here for a critique: https://gist.github.com/no-defun-allowed/7e3e238c959e27d4919...