Why This Recipe Works

For our version of this classic French pairing, we started by building a flavorful base for the lentils, gently cooking onion, carrots, and celery in olive oil until soft. Fruity tomato paste and plenty of garlic added even more depth before the lentils and water went in. When the lentils were fully softened and most of the moisture in the pot had either evaporated or been absorbed, we set them aside to focus on the salmon, which we'd briefly brined in a saltwater solution to season the fish and to ensure that it retained plenty of moisture as it cooked. Unconventionally, we placed the salmon skin side down in a cold nonstick skillet that had been strewn with salt and pepper. As the pan heated up, the salmon began to release some of the fat that lies just beneath the skin, crisping it, and enabling us to cook the fish without any additional fat. A bit of mustard and sherry vinegar stirred into the lentils brightened their flavor, making them an ideal pairing for the rich fish, and a final addition of extra-virgin olive oil added grassy top notes.

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Before You Begin

To ensure uniform cooking, buy a 1½-pound center-cut salmon fillet and cut it into four pieces. Using skin-on salmon is important here, as we rely on the fat underneath the skin as the cooking medium. If using wild salmon, check for doneness earlier and cook it until it registers 120 degrees. Small, olive-green lentilles du Puy are worth seeking out for their meaty texture, but if you can't find them, substitute another small green lentil. Do not use red or brown lentils. We used Diamond Crystal kosher salt. If using Morton kosher salt, use only 1 teaspoon in the lentils; 3 tablespoons for brining the salmon; ⅜ teaspoon in the skillet; and ⅛ teaspoon on the salmon.

Instructions

for the lentils

Heat 1 tablespoon oil in medium saucepan over medium heat until shimmering. Add onion, celery, carrot, and salt and stir to coat vegetables. Cover and cook, stirring occasionally, until vegetables are softened but not browned, 8 to 10 minutes. Add garlic, tomato paste, thyme, and pepper and cook, stirring constantly, until fragrant, about 2 minutes. Stir in water and lentils. Increase heat and bring to boil. Adjust heat to simmer. Cover and cook, stirring occasionally, until lentils are tender but not mushy and have consistency of thick risotto, 40 to 50 minutes. Remove from heat and keep covered.

for the salmon

While lentils are cooking, dissolve ¼ cup salt in 1 quart water in narrow container. Submerge salmon in brine and let stand for 15 minutes. Remove salmon from brine and pat dry with paper towels. Allow to stand while lentils finish cooking.

Sprinkle bottom of 12-inch nonstick skillet evenly with ½ teaspoon salt and ½ teaspoon pepper. Place fillets, skin side down, in skillet and sprinkle tops of fillets with remaining ¼ teaspoon salt and remaining ¼ teaspoon pepper. Heat skillet over medium-high heat and cook fillets, without moving them, until fat begins to render, skin begins to brown, and bottom ¼ inch of fillets turns opaque, 6 to 8 minutes.

Using tongs and thin spatula, flip fillets and continue to cook without moving them until centers are still translucent when checked with tip of paring knife and register 125 degrees (for medium-rare), 5 to 8 minutes longer. Transfer fillets, skin side up, to clean plate.

Warm lentils briefly if necessary. Stir in vinegar, mustard, and remaining 1 tablespoon oil. Season with salt, pepper, and vinegar to taste. Divide lentils among wide, shallow serving bowls. Arrange salmon skin side up on lentils and serve.