Started in a cold pan, which sounds wrong and is the entire trick. The fat renders slowly and the skin ends up like glass.
Dry the skin thoroughly with paper towel and salt it. If you have an hour, leave it uncovered in the fridge — this matters more than anything else here.
Lay the thighs skin down in a cold, dry, heavy pan. Turn the heat to medium-low. Walk away for 18 minutes.
The skin should be deep amber and release without sticking. If it sticks, it isn't ready. Turn them over.
Add the garlic, thyme, lemon slices and stock. Simmer 12 minutes until the thighs are cooked through and register 175°F at the bone.
Lift the chicken out, reduce the pan juices for two minutes, add the lemon juice, and pour around — never over — the chicken.