Chop spinach coarsely, and remove root ends and, if desired, stems. (These were tender enough to keep.) Wash carefully to remove sand, then dry.

Melt a little butter in a pan, Add the spinach, and stir lightly until is starts to soften and shrink a little. Push it to the side.

Add more butter if needed. Place the filets in the pan. Cook about 2-3 minutes, until the outside facing the pan is cooked but the center is still uncooked, turn over. Cook another 3-6 minutes, or as needed to cook through - be careful not to overcook.

While fish is cooking, stir spinach occasionally. Remove from pan when done to taste. Remove fish when done.

Add vinegar to pan and deglaze. Pour over fish.

Grate nutmeg over fish and spinach.

Serve at once.