Bring a large pot of water to a boil and add salt. Add the potatoes and cook until tender, about 15 minutes. Drain and set aside. Put the butter in a deep skillet or flameproof casserole dish. Turn the heat to medium-high and wait about a minute until the butter melts. Add the chicken, skin side down, and brown it well, rotating and turning the pieces as necessary, 10 to 15 minutes. Remove the chicken from the skillet and set aside. Reduce the heat to medium-low and add the garlic, scallions, and dill. Stir until the garlic is softened, about 1 minute. Add the potatoes to the skillet and stir to coat with the herb mixture; add the chicken pieces and stir again. Turn the heat to low and add the sour cream. Simmer for another 10 minutes.