In a 4-quart Dutch oven, cook onion in oil until tender. Add tomatoes and pancetta. Bring to boiling. Reduce heat; simmer, uncovered, about 45 minutes or to desired consistency; stir occasionally.
Stir in basil and pepper. Serve over pasta. Freeze leftovers in airtight freezer containers up to 3 months; thaw overnight in refrigerator and reheat to serve. Makes 8 servings.