As said by Jeremy, DSS stores all configuration modifications in an internal git repository. This repository is not exposed in the GUI. Everything that follows is not officialy supported, so before touching anything in the git repository, backup the DATA_DIR.
Any intervention on this git repository should be done with DSS stopped. If things go wrong, you must restore the DATA_DIR from the above backup.
Alternatively, you could try this read-only (and thus safer) access to the git repository, to display the code this recipe used:
# look for the sha1 of the commit which deleted the recipe, for instance “commit 424242424242”
# Quit this display by typing “q”
git show --name-only 42424242 # where 42424242 is the beginning of above commit sha1
# note the .py file containing the python code to recover, for instance projects/FOO/recipes/bar.py
git show 42424242^:projects/FOO/recipes/bar.py
# mind the starting circumflex: it asks git to look for this file in commit just before deletion
This displays the deleted code. It should now be straightforward to recreate the recipe and copy paste the code.
Hope this helps,