Heat olive oil in a large nonstick skillet over medium-high heat. Sprinkle chicken evenly with pepper. Add chicken to pan, and cook 6 minutes on each side. Remove from pan, and keep warm.
Add mushrooms and leek to pan; sauté 8 minutes. Return chicken to pan. Add wine, broth, sherry, and salt; cook 2 minutes or until chicken is done. Remove from heat; stir in sour cream. Serve over noodles. Garnish with parsley, if desired.