Cut the fish fillets into 3 parts each. Puree the basil in the oil.
Leave the butter out, bring to the boil with the broth. Poach the fish pieces on each side for 3 minutes. Then take out, season with salt and pepper, arrange on plates and keep warm.
Reduce the brew with cream. Stir in the basil paste and crème fraîche, season with salt and pepper.