Preheat oven to 400°F (200°C).
Score the duck skin in a crisscross pattern without cutting into the meat. Season both sides generously with salt, pepper, and thyme.
Heat a cast-iron or oven-safe skillet over medium heat. Place the duck breasts skin-side down in the cold pan (no oil needed yet—duck will render its own fat).
Slowly render the fat, about 5–7 minutes, until the skin is crisp and golden. Pour off excess fat if needed (save it for roasting veggies later!).
Flip the duck, add garlic cloves to the pan, and sear the other side for 1–2 minutes.
Transfer the skillet to the oven and roast for 5–7 minutes, or until the duck reaches desired doneness (135°F for medium-rare).
Rest for 5–10 minutes before slicing. Drizzle with optional balsamic or lemon juice for a bright finish.