SERVES 6 – 8

This recipe was invented by resourceful Basque fishermen, who had to create dishes out of the staples they most often had on hand, namely, potatoes, dried peppers, and fish. The name derives from marmita, the Spanish word for the type of pot in which the stew was prepared.

6 dried choricero peppers or new mexico chiles, seeded
2 lbs. mussels, debearded and scrubbed
10 tbsp. extra-virgin olive oil
2 medium white onions, thinly sliced
5 large yukon gold potatoes (about 4 lbs.), peeled and
   cut into 1 1⁄2" chunks
5 cups fish stock
3 plum tomatoes, cored and chopped
2 lbs. boneless skinless tuna filets, cut into 2" chunks
Salt and freshly ground white pepper

1. Bring a pot of water to a boil over medium heat, add peppers, and cook, covered, until soft, 40–45 minutes. Drain. Scrape pulp from peppers and discard skins; transfer pulp to a bowl. Put mussels into a pot, cover, and cook over medium-high heat, shaking occasionally, until mussels open, 5–7 minutes (discard any that don't open). Set aside for 10 minutes. Strain through a fine-mesh sieve over a bowl to collect mussel broth. (Reserve mussels for another use.)

2. Heat 7 tbsp. oil in a pot over medium heat. Add onions; cook until browned, 20–25 minutes. Add potatoes; cook until somewhat softened, 10–12 minutes. Add reserved pepper pulp; cook until fragrant, 2–3 minutes. Add mussel broth and fish stock; bring to a boil. Reduce heat to medium-low and simmer, partially covered, until potatoes are tender, 12–15 minutes. Add tomatoes; cook for 10–12 minutes. Working in batches, fry tuna in remaining oil in a large skillet over medium-high heat, turning, until golden yet rare, 2–3 minutes. Add to pot; remove from heat and let rest for 5 minutes. Season with salt and pepper to taste.