Hake or cod cheeks in salsa verde are one of the most adored dishes in Basque country. The version here, adapted from chef Francis Paniego, calls for cod fillet instead. Slideshows: More Cod Recipes
In a large skillet, warm 1/3 inch of oil over moderate heat. Add the potatoes, onion and a generous pinch of salt and cook, stirring occasionally, until browned, about 20 minutes. Using a slotted spoon, transfer the potatoes and onion to 4 bowls; keep warm.
Strain the oil through a fine sieve into a heatproof bowl, then return it to the skillet. Add the garlic and cook over moderately low heat until golden, 5 minutes. Discard the garlic. Add the cod to the skillet and cook, turning once, until just white throughout, 7 minutes. Using a slotted spoon, add the cod to the potatoes.
Pour off all but 1/3 cup of the oil from the skillet and let cool slightly. Stir in the 1/4 cup of oil and the water and bring to a simmer over moderate heat. Stir in the parsley and season with salt. Spoon the salsa verde over the fish and potatoes and serve.
Try it with a floral rosé from Rioja.