Season the chicken thighs all over with salt and pepper.

Heat the oil in a deep-sided large skillet set over medium-high heat. Add the chicken thighs, skin-side down, to the heated oil and cook for about 5 minutes; flip and cook for 4 to 5 more minutes or until just browned.

Remove the chicken from the skillet and transfer to a plate; set aside.

Add the sliced onions to the skillet and cook for 2 to 3 minutes or until softened. Add more oil if needed. Stir in the garlic and cook for 10 seconds. Add anchovies and pepper flakes, and continue to cook for 2 more minutes, stirring occasionally.

Stir in the tomato paste until dissolved. Then, stir in the crushed tomatoes, scraping up any browned bits from the bottom of the skillet. Mix in the olives and capers.

Return the chicken thighs back to the skillet. Continue to simmer for about 15 to 20 minutes or until the chicken is cooked through. If the sauce begins to look dry at any point, add a couple tablespoons of chicken broth or water.

Remove from heat and garnish with chopped parsley.

Serve the chicken thighs with the puttanesca sauce.