In a small bowl, combine fish sauce and sugar; set aside.
In a large skillet over medium heat, heat oil. Place the chicken in the skillet, skin side down, and brown well, turning once, about 8 - 10 minutes total. Remove the chicken from the skillet and keep warm.
Add shallots or onion and stir until translucent, 1 to 2 minutes.
Add fish sauce-sugar mixture and stir until sugar caramelizes and turns golden brown. Add the chiles, ginger and black pepper, and stir for 2 minutes. Add stock, raise heat to high, and bring to a boil.
Add chicken, reduce heat slightly, and continue to cook, stirring frequently, until sauce is reduced and thickened and the chicken is cooked through, about 10 more minutes.
Place two thighs on each plate, spoon a little of the sauce over the top and garnish with sliced scallions and lime. Serve with jasmine rice.