Heat two tablespoons of oil in a large Dutch oven over medium high heat. Season ribs with salt and pepper.
Add ribs to the pan in batches and brown on all sides. Remove to a paper towel lined plate and set aside.
Add onions, carrots, celery, and garlic to the crock of a slow cooker. Season with salt and ground black pepper. Nestle pork ribs in the vegetable mixture.
In a separate bowl, combine tomato paste, vinegar, and red pepper flakes, beer and chicken broth. Pour mixture over the top of the pork ribs. Add the bay leaves.
Cook on high for 4 hours or low for six hours.