Season the ribs with salt & pepper.
Broil them 6 inches from the broiler for 10 minutes or till they're well browned turning once.
Place the ribs in the crock pot.
Combine the salsa, hot sauce, chili powder, & beef stock in a bowl. Mix well. Pour this over the ribs.
Cover and cook on low for 6 hours or on high for 3 hours.
Transfer the ribs to a platter. Keep them warm. Leave the liquid in the pot. Skim off any fat.
With crock pot on high, put 1/2 of the onion rings in the liquid and cook it 10-15 minutes or until slightly thickened.
Pour the thickened sauce over the ribs.
Sprinkle the remaining onion rings over the ribs.
If desired, drizzle more hot sauce to taste over the ribs.