Pat the chicken thighs completely dry with paper towels to ensure a crisp sear.
Season both sides of each chicken thigh evenly with the kosher salt and black pepper.
Heat the olive oil in a 12-inch heavy skillet over medium-high heat until it shimmers.
Lay the chicken thighs smooth-side down in the hot skillet without crowding them.
Cook undisturbed for 6 to 8 minutes until the bottoms turn deep golden-brown.⏱ 8 min
Flip the thighs over with tongs and cook the second side for another 5 minutes.⏱ 5 min
Transfer the chicken to a warm plate, leaving the rendered drippings in the skillet.
Lower the heat to medium and stir the minced garlic into the skillet for 30 seconds until fragrant.⏱ 30 sec
Pour in the chicken broth and lemon juice, scraping up all browned bits stuck to the pan.
Simmer the liquid steadily for 2 minutes until it reduces in volume by about half.⏱ 2 min
Turn off the heat entirely and swirl the cold butter cubes into the pan until glossy and emulsified.
Return the chicken and any resting juices to the skillet alongside the fresh lemon slices.
Spoon the warm pan sauce all over the chicken, scatter with fresh parsley, and serve immediately.