Curried Scallops with Spinach

Ingredients 
 2 tablespoons butter 
 1 onion, chopped 
 1/2 teaspoon salt 
 2 teaspoons curry powder 
 2 teaspoons tomato paste 
 1/2 cup canned low-sodium chicken broth or homemade stock 
 1 cup light cream or half-and-half 
 2 cups shredded spinach (about 3 ounces spinach leaves) 
 2 pounds sea scallops 

 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. 
 Transfer the onion mixture to a blender and add the tomato paste, broth, and cream. Puree until smooth. Return the sauce to the pan. 
 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.