Cook bacon in a large skillet until crisp. Remove from skillet, reserving bacon drippings. Drain bacon on paper towels. Set bacon aside.
Sauté liver and onion in reserved bacon drippings 5 minutes. Combine sour cream, mushrooms, salt, and pepper; add to liver mixture, stirring gently, until well combined. Cover and bake at 325° for 30 minutes.
Transfer liver to a warm serving platter. Spoon pan liquid over liver. Top with bacon slices, and sprinkle with paprika.