Pat the chicken thighs dry and season generously with salt and pepper.
Heat a large skillet over medium heat and add olive oil, waiting until it shimmers slightly.
Place the chicken thighs skin-side down in the skillet. Sear for about 7-8 minutes, until the skin is golden and crispy, then flip and cook for another 5 minutes. Remove and set aside.
Add sliced onions to the skillet and cook, stirring occasionally, until they soften and turn golden brown, about 6 minutes.
Add the sliced apples to the skillet and cook for 3-4 minutes, until they start to soften and release their aroma.
Sprinkle chopped thyme over the mixture and stir gently to combine.
Return the chicken to the skillet, skin-side up, nestling it among the apples and onions. Pour chicken broth around the sides if using, to help deglaze and add moisture. Cover loosely and cook over low heat for 15-20 minutes, until the chicken is cooked through and the flavors meld.
Uncover the skillet and increase the heat to medium. Let cook for another 3-5 minutes until the sauce slightly thickens and the chicken skin is crispy again.
Check seasoning and adjust with salt and pepper as needed. Serve the chicken hot, spooning the caramelized apples and onions alongside.
