Pick the stems from the spinach and remove any bad leaves. Wash the spinach in several changes of clean water, till no more dirt come out.
Move the spinach, still dripping, into a large saucepan set over medium-low heat. Cook the spinach, uncovered, until it wilts. The water that clings to the leaves will be enough to cook it with. Remove the spinach and, after it cools enough to handle, squeeze all the excess water out of it. Chop it coarsely and set aside.
While the spinach is cooking, rinse the salmon fillets. Combine the marinade ingredients in a wide bowl. Let the salmon fillets marinate for a minute on each side. Place the salmon, dripping marinade, on a greased broiler pan. Place three inches under the heat source in the broiler for three minutes. Turn the fish and top with a few flecks of butter. Cook for another two to three minutes, then remove and keep warm.
Melt the remaining butter in a saucepan over very low heat. Whisk in the dill, lemon juice, salt, pepper, and nutmeg. When well blended and creamy-looking, remove from heat.
Return the spinach to the pot you cooked it in, now over medium-low heat. Add the cream, lower the heat to low, and cook, stirring, until everything is combined and heated through.
Divide the spinach among four serving plates and lay the salmon athwart the spinach. Spoon some of the butter sauce over the top and serve.
