Season all sides of pork with salt and pepper
Set Slow Cooker to High (will take about 3 1/2 hours to slow cook pork should on high setting)
In a large heavy pot, heat 3 tbsp of oil until hot.
Add pork shoulder, fat side down. Sear until brown. Turn and sear all sides until nice and brown.
While pork is browning, add coarsely sliced onions, garlic and bay leaf to slow cooker.
Once browned, add pork shoulder to slow cooker.
Pour Bernard's Tomatillo y Poblano Cooking Salsa over pork shoulder.
Fill emptied salsa jar with chicken stock and stir. Pour chicken stock and remaining salsa into slow cooker.
Slow cook a total of 3 1/2 hours on high heat setting. At 2/12 hours, baste with juices. Cook for another 30 minutes. Check to see if additional basting necessary.
At 3 1/2 hours, check pork shoulder. Bone should be easy to remove. If not, baste and cook an additional 30 minutes.
Remove cooked pork shoulder to plate. Reserve cooking liquid, skimming fat from top layer. Place remaining juices into heavy pot over medium high heat and reduce by half
While juices reduce, add pork back to slow cooker. Shred with two forks and keep warm.
Pour 1/2 reduced cooking juice over shredded pork and mix. Use remaining juice to add as a topping. Let rest 15 minutes before serving.