Slow Cooker Beef and Black-bean chili

from Everyday Food

1 lb beef chuck, cut into chunks
1 can (15 oz) tomato puree
1 c. dried black beans, rinsed
1 medium red onion, chopped
2 garlic cloves, minced
3 T chili powder
ground cumin to taste (about 1 tsp)
salt and pepper
1/4 c. sour cream

Combine beef, tomato puree, beans, onion, garlic, chili powder, cumin, 2 c. water, 2 tsp salt, and 1/2 tsp pepper. Cover, and cook on high, 6 hours (low 8 hours). Serve with sour cream and chopped onion.