In a large resealable plastic bag, combine the flour, salt, paprika and pepper. Add fish and shake to coat (if using fillets, cut into serving-size pieces first).
In a skillet, saute onion in butter until tender; remove and set aside. Add fish to the skillet, cook over medium heat for 3-5 minutes on each side or until the fish flakes easily with a fork. Remove fish to a serving plate and keep warm.
Add the sour cream, basil and onion to the skillet; heat through (do not boil).
Serve over fish. Garnish with parsley.
NOTE: Haddock or salmon fillets or steaks can be used. I didn't have fresh parsley, so I used dried.