Pat the chicken thighs dry with paper towels. Season both sides with kosher salt and black pepper.
Heat olive oil in a large oven-safe skillet over medium-high heat until shimmering.
Place the chicken thighs skin-side down in the skillet and cook without moving for 7-8 minutes until the skin is golden brown and crispy.
Flip the chicken thighs and immediately place a heavy cast-iron skillet or another heavy pan on top of the chicken to press it down.
Reduce heat to medium and cook for an additional 10 minutes, maintaining the weight on top of the chicken to ensure even cooking.
Remove the top skillet carefully and transfer the chicken to a plate, tenting with foil to keep warm.
Add minced garlic to the skillet and sauté for 30 seconds until fragrant.
Pour in the chicken broth and lemon juice, scraping the bottom of the skillet with a wooden spoon to release any browned bits.
Simmer the sauce for 3-4 minutes until slightly reduced.
Remove the skillet from heat and whisk in the unsalted butter and fresh thyme leaves until the sauce is smooth and glossy.
Return the chicken to the skillet and spoon the lemon pan sauce over the top before serving.