Step 1 (5 minutes): Pat chicken thighs dry and season generously with salt and black pepper. Slice mushrooms. Thinly slice the leek (white and light green parts only) and carrots. Dice the onion and mince the garlic. Chop the fresh parsley.

Step 2 (5 minutes): Heat olive oil in a large, deep skillet or Dutch oven over medium-high heat. Add the chicken thighs skin-side down (if applicable) and sear for 5 minutes until golden brown. Flip and sear for another 2 minutes. Remove chicken from the pan and set aside.

Step 3 (8 minutes): Add the sliced mushrooms to the skillet and sauté for 5 minutes until they release their moisture and start to brown. Add the diced onion, sliced leek, and carrots to the skillet. Sauté for 3 minutes until the vegetables begin to soften.

Step 4 (5 minutes): Stir in the minced garlic and cook for 1 minute until fragrant. Pour in the chicken broth. Return the seared chicken thighs to the skillet, nestling them among the vegetables. Bring to a simmer, then reduce heat to medium-low, cover, and cook for 5 minutes, or until chicken is cooked through and vegetables are tender. Stir in fresh parsley before serving.