Jess Black (A Dish Served Cold)
Start at the Baron Lumber Mill, an Outpost in Jacob's Region, and a prerequisite for recruiting Jess Black. There are lots of sniper perches and catwalks here ( a perfect outpost to attack with Jess, if you somehow already had her).
As it is, you can do pretty well for stealth by sniping from the wooded hill north of the site- just remember to keep changing positions. You might also want to keep Grace or Peaches on standby for any hostiles that get away from you. This is particularly true for the lone heavy mixed into the bunch here. If you miss your first shot, call up a pro for the second
Killing the last hostile completes the location.
You'll see Jess freed in the liberation cutscene. Note that, right by where she starts out, is a table with a regional map and a key. It's worth grabbing both.
Talk to Jess to start her recruitment mission - A Dish Served Cold.
Follow Jess through the wild, while listening to her progressively more gruesome reminiscence. You'll encounter hostiles periodically. The first group is just three no-goods around a campfire, but the second group has three hostages in cages.
Take out the hostiles as quietly as you can. Raise a ruckus and they'll start killing hostages. This doesn't seem to have any effect of gameplay, mind, but it's poor form.
Note that one of the hostiles here is a heavy, so may need special attention. When the cultists are down, free the hostages, and set off with Jess again.
The next camp also has three hostages, but watch out for the sharpshooter, who has spectacular night vision.
Free the hostages, loot the camp, and then follow Jess as she relates the worst part of the story yet. When that's finally over with, you'll reach the Cook himself.
After all that setup, the Cook is just a standard-issue flamer. Target his fuel tank to blow him up, then pick off any goons left standing.
Talk to Jess afterwards to unlock her as a companion, and complete the mission.