These notes are based on https://wiki.debian.org/BuildingFormalBackports

Create a cowbuilder image. If you are already using cowbuilder for other stuff, you must specify where the base will be and the distribiution where you want to backport:

$ sudo cowbuilder --create --basepath /var/cache/pbuilder/base-jessie.cow --distribution jessie

Add an entry to changelog

$ dch --bpo

Build the backport:

$ gbp buildpackage --git-pbuilder --git-ignore-new --git-dist='jessie' -d -vSTABLE_VERSION

where STABLE_VERSION is the stable version or the last backport.

Upload the package

$ dput PKG_NAME*changes