Chicken Breasts Dijon


2 tbsp olive oil - 4 skinless, boneless chicken breasts (about 1 & 1/2 pounds) - Kosher salt and freshly ground black pepper - 2 small leeks, white and pale-green parts only, thinly sliced (about 1/2 cup) - 1 small onion, minced (about 1/2 cup) - 4 garlic cloves, minced - 2 cups low-salt chicken broth - 1 cup dry white wine - 1/2 cup Dijon mustard - 2 tablespoons minced fresh thyme plus thyme leaves for garnish - 1 tablespoon butter

Heat oil in a large heavy Dutch oven over medium-high heat. Season chicken breasts with salt and pepper. Place chicken in Dutch oven and cook until brown on both sides, 12-15 minutes total. Transfer to a plate and set aside.

Place leeks and onion in same pot and sauté until tender, about 8 minutes. Add garlic and sauté until tender, about 2 minutes. Stir in broth, wine, Dijon mustard, and minced thyme and bring to a simmer. Return chicken to pot. Cover and simmer over medium-low heat until chicken is cooked through, about 15 minutes.

Transfer chicken to plates. Bring liquid in pot to a boil; cook until sauce is thickened and glossy, about 15 minutes. Whisk in butter and season with salt and pepper. Spoon sauce over chicken and garnish with thyme leaves.