Preheat the oven to 200°C (400°F).
Pat the chicken thighs dry with paper towels and season both sides with the salt and pepper.
Heat a cast iron skillet over medium-high heat until hot, then add the olive oil and butter and swirl to coat.
Place the chicken thighs in the skillet skin-side down and cook undisturbed for 6–8 minutes, until the skin is golden brown and crispy.
Flip the thighs, add the minced garlic to the pan, then transfer the skillet to the preheated oven.
Bake for 12–15 minutes, or until an internal temperature of 74°C (165°F) is reached.
Remove the skillet from the oven and let the chicken rest for a few minutes before serving.