Rinse the spinach carefully.
Bring plenty of salted water to the boil. Put the spinach in and blanch for just 1 minute until it has collapsed. Drain the water, rinse when cool, squeeze well and chop coarsely.
Peel and chop the onion and garlic clove. Sauté in the warmed butter. Sprinkle with the flour and sauté briefly. Then slowly add the soup and vermouth while stirring. Add the spinach and make the soup with the lid closed for 10 minutes.
Finely blend the soup with a hand mixer. Add the cream, let it boil and season the soup with salt, pepper and freshly grated muscatel.
Immediately before serving, cut the salmon fillet into 4 even pieces.
Season with salt and pepper and fry in hot olive oil for a good 1 minute on all sides. The salmon pieces should still be almost raw inside.
Arrange the soup in heated deep plates and place 1 slice of salmon in each. Serve immediately.
Tip: Did you know that one bowl of spinach provides about 50 percent of your magnesium needs?