For the Picada:
Add the potatoes, wine, and enough stock to cover the potatoes, then add salt to taste, the saffron, and the sugar and simmer, covered, over low heat for about 20 minutes, until the potatoes are just tender.
Meanwhile, for the picada, fry the almonds and garlic clove in the oil in a small skillet until both are lightly brown; drain on paper towels. The usual way is to crush and grind these to a paste in a mortar with the parsley, but you can use a food processor; add a ladleful of the stock to dilute it.
Put the fish in the soup and cook for 3 minutes (5 minutes if using monkfish). Add the shrimp and picada and cook until the shrimp turn pink and the fish is opaque throughout.
Claudia Roden is a chef, food writer and author. She has written several books on Middle Eastern and Mediterranean cuisine, most recently The Book of Jewish Food, which won a James Beard award.