The hatchbox article referenced in an earlier post says to create a custom build script which will run Jekyll to use git to create the static site (after you push a new version to Hatchbox).

The instructions on the Hatchbox link are somewhat out of date, for some reason “bundle exec” is now required to avoid a “jekyll not found” error.

So the Custom Build script is:

bundle install
bundle exec jekyll build --destination public