Mix garlic, brown sugar, thyme, rosemary, allspice, salt, and pepper together in a bowl. Pat chicken dry and rub with the spice mixture. Refrigerate for 30 minutes.

Heat olive oil in a skillet over medium-high heat. Add chicken thighs, skin-side down, and cook until crisp, about 4 minutes. Flip. Pour chicken stock around the thighs. Squeeze juice of 1 lemon into the skillet. Slice the second lemon and arrange over the thighs.

Cover and simmer until chicken is no longer pink at the bone and the juices run clear, about 30 minutes. An instant-read thermometer inserted near the bone should read 165 degrees F (74 degrees C). Discard lemon slices and serve.