In a blender puree the pimiento with the cayenne, season the puree with salt, and reserve it in a bowl. In a saucepan cook the spinach with the water clinging to its leaves over moderate heat, covered, until it is wilted, transfer it to the blender, cleaned, or a food processor, and puree it with 2 tablespoons water. In the pan heat the spinach puree with the butter over moderately low heat, stirring occasionally, until the butter is melted and keep the puree warm, covered. In a heavy saucepan large enough to hold the cod in one layer combine the cod with enough salted cold water to cover it by 1 inch, bring the water to a simmer, and in it poach the cod, covered, at a bare simmer for 5 to 6 minutes, or until it is just flakes. Divide the spinach puree between 2 plates, spoon dollops of the pimiento puree onto the spinach puree, and swirl them decoratively into the spinach puree. Transfer the cod with a slotted spatula onto the purees. Serves 2. Gourmet September 1991