Pat the chicken breasts dry with paper towels to remove excess moisture.
In a small bowl, mix together kosher salt, black pepper, garlic powder, and smoked paprika.
Season both sides of each chicken breast evenly with the spice mixture.
Heat the olive oil in a cast iron skillet over medium-high heat until shimmering but not smoking, about 2 minutes.
Place the chicken breasts in the skillet and cook without moving for 6-7 minutes until the underside is golden brown and releases easily from the pan.
Flip the chicken breasts over and add the butter, smashed garlic cloves, and fresh thyme to the skillet.
Tilt the skillet slightly and spoon the melted butter and aromatics over the chicken breasts repeatedly for 5-6 minutes, or until the internal temperature reaches 165°F (74°C).
Remove the chicken breasts from the skillet and transfer to a plate. Let rest for 5 minutes before slicing and serving.