In a small food processor combine the garlic, rosemary, thyme, salt and pepper. Add the olive oil and brown sugar process until it forms a paste, scraping down the sides. Stir in the Dijon mustard (if you are using coarse mustard you want to stir it in rather than process it so the mustard seeds stay coarse). Rub the paste all over the pork shoulder, loosely cover it with plastic wrap, and refrigerate from 2 to 24 hours.

Place the pork in the slow cooker, pour in the beer around the sides (try not to clean off the marinade). Set it for 8 hours on low.

Remove the meat from the slow cooker (it may start to fall apart, which is fine). Let the meat sit for about 15 minutes. When the pork has finished sitting, use two forks or your fingers to pull the pork apart into chunks as small or large as you like.