Saumon Aux Lentilles (Pan-Seared Salmon with Braised Lentilles Du Puy)

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.