Place the onions and garlic in the bottom of a slow cooker insert.
In a small bowl, combine the chili powder, salt, cumin, coriander, pepper, paprika and brown sugar. Rub the pork shoulder with the spice rub on all sides.
Place the seasoned pork shoulder with the fat side up on the bed of onions in the slow cooker. Pour in the lager and chicken stock.
Cover and set the slow cooker for 6 hours on high or 10 hours on low, or until the pork is fork tender and coming apart.
Once cooked, carefully transfer the pork to a cutting board. Shred the pork using two forks, and discard any fat.
Place shredded pork and cooked onions in bowl and season with salt and pepper.
Strain the liquid remaining in the slow cooker and use a bit of this liquid to keep the pulled pork moist.
Recipe by Big City Tiny Kitchen at https://bigcitytinykitchen.com/beer-braised-slow-cooker-pulled-pork-sandwich/