This is a very approachable paper from 1990 on one way to do it with a C kernel bootstrapping to Common Lisp: https://www.softwarepreservation.org/projects/LISP/kcl/paper... Kyoto Common Lisp (KCL) is the ancestor of today's Embeddable Common Lisp (ECL).

SICL is probably the best modern version of CL written in CL from a design standpoint, even if it's not taking over SBCL's role anytime soon: https://github.com/robert-strandh/SICL It uses some fancy bootstrapping to have the whole language available early, e.g. their definition of class 'symbol is:

    (defclass symbol (t)
      ((%name :reader symbol-name)
       (%package :reader symbol-package))
      (:metaclass built-in-class))

vs SBCL:

    (define-primitive-object
        (symbol :lowtag other-pointer-lowtag
                :widetag symbol-header-widetag
                :alloc-trans %make-symbol
                :type symbol)
      ...
      (name :ref-trans symbol-name :init :arg)
      (package :ref-trans symbol-package
               :set-trans %set-symbol-package
               :init :null)
      ...)

(That's from one of the papers from the 2019 European Lisp Symposium: https://www.european-lisp-symposium.org/2019/index.html Scroll down to the bottom for proceedings with all the papers in the pdf. Going through the ELS archives and checking out papers and their references can be useful for learning more about this stuff too.)