Wash the fish, pat dry and drizzle with the lemon juice.
Heat the herb butter in a pan and fry the fish steaks in it on both sides for about 5 minutes, then season with salt and pepper. Take out, wrap in aluminum foil and keep warm.
Clean, wash, dry and cut the fennel into thin slices. Set aside the fennel greens for garnish.
Heat the frying stock again and fry the fennel in it. After about 3 minutes, pour the white wine over everything and let it steep for another 3 minutes. Mix the crème fraîche with the mustard and add to the vegetables.
Arrange the fish with the fennel vegetables on plates, garnish with fennel greens and