Step 1 In a covered pot, steam the potatoes over rapidly boiling water until tender, about 10 minutes.
Step 2 In a large, heavy pot over medium-low heat, warm the oil and add the chorizo. Cook until it has rendered some of its fat and looks cooked, about 5 minutes. Add the onion and bell pepper and cook until softened, about 5 minutes. Add the garlic and cook until fragrant, about 3 minutes. Add the tomatoes, white wine and saffron and cook until the tomatoes have melted into the sauce, which should have lost its alcohol smell. Add the potatoes. The texture should be loose and slightly soupy, but not broth-like. Taste and season with salt. (The recipe can be prepared to this point up to 2 hours in advance; or even further if tightly covered and refrigerated.)
Step 3When almost ready to serve, warm the base over medium heat. Add the monkfish and cook just until it changes color, about 3 minutes. Add the clams, raise the heat to high, cover tightly and cook until all of the clams have opened, about 5 minutes. Sprinkle with parsley and serve immediately.