While cooking in this rich, pungent mustard sauce, leeks become velvety. Top mashed potatoes.
– 3 tablespoons grapeseed or avocado oil, divided – 1 pound boneless, skinless chicken thighs, trimmed – ¾ teaspoon salt, divided – ½ teaspoon ground pepper, divided – 12 ounces mixed mushrooms, coarsely chopped
– 2 cups sliced leek (1 medium), rinsed well – 2 cloves garlic, minced – 2 teaspoons chopped fresh thyme or tarragon, plus more for garnish – 3 tablespoons all-purpose flour – 3 cups low-sodium chicken broth – 2 cups frozen pea – 1 tablespoon Dijon mustard
Place 1 tablespoon oil in a big pot over medium heat. Thoroughly dry chicken and season with 1/4 teaspoon salt and pepper. Cook the chicken for 6–8 minutes on both sides in the pot. Get a clean plate.
Add mushrooms and the remaining 2 tablespoons oil to the pan and heat until lightly browned, 4–6 minutes. Occasionally stir in leek and simmer until barely softening, about 4 minutes. For 1 minute, saute garlic and thyme (or tarragon) until fragrant. Stir flour into the mixture for 1 minute.
Simmer broth on high, scraping away any browned pieces. Manage heat to simmer. Return chicken and liquids, cover, and cook until an instant-read thermometer inserted in the thickest part of a thigh registers 165 degrees F, about 10 minutes. Finish with 1/2 teaspoon salt and 1/4 teaspoon pepper.
Place chicken on platter. Uncover the sauce and heat peas and mustard for 2 minutes. Optional: Pour the sauce over the chicken and top with thyme or tarragon.
Tips Sunlight makes mushrooms one of the few vitamin D-rich foods. Dark-grown mushrooms have less D than wild ones.