1. In a large frying pan, melt the butter over moderately low heat. Add the onion and salt and cook, stirring occasionally, until the onion starts to soften, about 3 minutes. Stir in the curry powder and cook for 1 minute.
2. Transfer the onion mixture to a blender and add the tomato paste, broth, and cream. Puree until smooth. Return the sauce to the pan.
3. Bring the curry sauce just to a simmer. Stir in the spinach and scallops. Simmer, covered, until the scallops are just done, 5 to 7 minutes.
Fish Alternatives: Shelled medium shrimp would be delicious simmered in the curry sauce. You can also use bay scallops instead of the larger sea scallops, in which case reduce the cooking time to three minutes.
Wine Recommendation: Sauvignon blanc is a perfect choice to serve with this dish. Its acidity will go well with the spinach and work beautifully with both the mild curry and the scallops. You'll find good possibilities from many continents: Try a bottle from California, New Zealand, or South Africa.