Build bookdown from pre-knitted markdown files

Dear all,

I am trying to use bookdown to collect large markdown files into a book format. Ideally, what I was considering doing is knitting each separate Rmd file and keeping the intermediate markdown files by adding keep_md: true to the yaml header of each Rmd file. I would then build the book with the intermediate markdown files. I thought this could be done with the "Knit and Merge" rendering approach (using bookdown::render_book("foo.Rmd", "bookdown::gitbook",new_session = TRUE)), as descirbed in https://bookdown.org/yihui/bookdown/new-session.html.

However, this still knits first each Rmd and then builds the book. Is there any way to just take the markdown files for building the book?

thanks for any help