I also occasionally code using pen an paper, when facing a tough problem. Drawing the systems out, then physically writing out the code verbatim is a great way

I also occasionally code using pen an paper, when facing a tough problem. Drawing the systems out, then physically writing out the code verbatim is a great way (for me at least) to develop a picture of the problem and develop a canonical solution. In addition to copying the code over, I also clean up and copy the notes over as documentation, either as comments in code or markdown.