Remove the chicken thighs from the refrigerator and pat them dry with paper towels.
In a small bowl, mix together the kosher salt, black pepper, garlic powder, and smoked paprika.
Season both sides of the chicken thighs evenly with the spice mixture.
Heat the olive oil in a 10-inch cast iron skillet over medium-high heat until shimmering.
Place the chicken thighs skin-side down in the skillet and cook without moving for 7 to 8 minutes, until the skin is golden brown and crispy.
Flip the chicken thighs over and add the minced garlic, fresh thyme leaves, and unsalted butter to the skillet.
Continue cooking for another 10 to 12 minutes, spooning the melted butter and garlic over the chicken occasionally, until the internal temperature reaches 165°F (74°C).
Remove the skillet from heat and let the chicken rest for 5 minutes before serving.