Directions

1. Trim off and discard root ends and tough green tops of leeks. Cut leeks in half lengthwise and rinse well, then cut crosswise into 1/2-inch-thick slices. Rinse chicken and pat dry. Scrub potatoes and cut into 1/2-inch cubes.
2. In a 5- to 6-quart nonstick pan over medium-high heat, melt butter. Add chicken and turn as needed to brown lightly on all sides, 4 to 5 minutes total; transfer to a small bowl.
3. Add leeks to pan; stir until limp, 3 to 4 minutes. Add broth, vermouth, chopped basil, lemon peel, and potatoes; cover and bring to a boil over high heat. Reduce heat and simmer 10 minutes. Lay chicken on vegetables in pan; cover and simmer until potatoes are tender when pierced and chicken is white in center of thickest part (cut to test), 10 to 16 minutes longer.
4. With a slotted spoon, return chicken to the small bowl. Add peas to leek mixture. In another small bowl, blend cornstarch and 1/4 cup water until smooth. Stir into pan and bring to a boil over high heat, stirring. Add salt and pepper to taste.
5. Spoon equal portions of the leek mixture into wide soup bowls. Top each mound of leeks with a piece of chicken (if desired, cut breasts crosswise into 1/2-inch-thick slices). Garnish with lemon slices and basil sprigs.