This is so interesting as I'm trying to speed up my lettering. I couldn't find a tutorial when I started lettering earlier this year so I just pipe little lines or dots of flood consistency, then drag the letter out using a scribe tool. It is not an advisable method as each cookie takes ~10 minutes or so. If you can have nice big text on a big cookie that's obviously preferable; I keep getting customers who want tiny writing on a little itty-bitty cookie. Thanks for the link Manu, I have a new technique to work toward.
I also make sure to pay the commercial license fee to the creator of any font I use.