Spaghetti with Halibut & Lemon

Combine halibut, lemon juice, oil, onion, parsley and crushed red pepper in a large bowl. Season with 1/2 teaspoon salt and mix well. Let stand at room temperature, stirring occasionally, until the fish is opaque throughout, at least 1 hour and up to 2 hours.

Place potato in a large saucepan, cover with cold water and bring to a boil. Reduce heat to medium and cook until very tender, 12 to 15 minutes. Remove the potato; peel when it's cool enough to handle. Keep the potato-cooking water and add enough water to the pot to make about 2 quarts total for cooking the pasta.

When the fish is done marinating, return the water to a boil. Add the remaining 1 tablespoon salt, then stir in pasta until all the strands are submerged. Cook according to package instructions until just tender.

Meanwhile, mash the potato through a ricer or with a fork. Add to the bowl with the fish and stir until well combined.

When the pasta is done, drain well and toss with the fish mixture. Serve at once.