如何将部分历史记录从git分支转移到新的存储库？

I recently joined a project that has a github repo with a branch that is effectively a fresh start of the entire source tree. I'd like to copy that one branch, starting from just from just that "new source tree" commit, to a new repo, without any remnants of the old source tree lingering in the repo (allowing for the repo to be much smaller). What are the steps to accomplish this?I recently joined a project that has a github r