1. Prepare the Chicken: Pat the boneless, skinless chicken thighs dry with paper towels. This helps them brown nicely. Season both sides generously with salt, black pepper, dried thyme, garlic powder, and onion powder. Make sure the seasonings are evenly distributed over the chicken.

2. Sear the Chicken: Heat the olive oil in a large, oven-safe skillet (cast iron or stainless steel works best) over medium-high heat. Once the oil is shimmering, add the seasoned chicken thighs to the hot skillet. Cook for 5-7 minutes per side, until deeply golden brown and cooked through. The internal temperature should reach 165 F (74 C). Remove the chicken from the skillet and set it aside on a plate, tented loosely with foil to keep warm.

3. Saute the Apples: Reduce the heat to medium. Add the sliced apples to the same skillet, scraping up any browned bits from the bottom of the pan. Cook the apples for 3-5 minutes, stirring occasionally, until they start to soften slightly and turn a light golden color. They should still have a bit of a bite.

4. Deglaze and Simmer the Sauce: Pour in the apple cider and chicken broth, stirring well to combine with the apples and any remaining pan drippings. Bring the mixture to a gentle simmer. Stir in the Dijon mustard and maple syrup. Let the sauce simmer for 2-3 minutes, allowing the flavors to meld.

5. Thicken the Sauce: In a small bowl, whisk together the cornstarch and cold water until smooth to create a slurry. Pour the slurry into the simmering sauce in the skillet, stirring constantly. Continue to cook and stir for another 1-2 minutes, until the sauce thickens to your desired consistency. It should be glossy and coat the back of a spoon.

6. Combine and Serve: Return the cooked chicken thighs to the skillet, nestling them among the apples and coating them with the thickened sauce. Heat for another minute or two to ensure the chicken is warmed through. Garnish with fresh chopped parsley, if desired, and serve immediately.