In a small bowl combine the prunes with the Scotch and 2 tablespoons of water and set aside. Season the chicken with 1 teaspoon of the salt and the pepper. Place a large Dutch oven or soup pot over medium heat and melt 2 tablespoons of the butter. Saute the chicken on each side until well-browned, about 10 minutes. Transfer the chicken to a plate, and pour off any fat left in the pan. Add the remaining butter to the pan, saute the leeks over medium-low until tender, about 25 minutes.

Tie the parsley, thyme, and bay leaf with a piece of kitchen twine. Add the herb bundle, the chicken and the broth to the pot. Bring to a boil, and then lower the heat to maintain a gentle simmer. Cover and cook the soup for until the chicken is cooked through and tender, about 25 minutes. Remove the chicken, set aside to cool slightly. Remove the herb bundle and discard. Skim any fat from the surface of the soup with a spoon or ladle, if needed. Remove the chicken meat from the bones and cut into 1-inch chunks. Add the chicken cubes, the prunes, and their liquid to the soup. Season with salt and pepper. Simmer for 2 minutes. To serve divide the soup evenly among 6 warm soup bowls.