5-3/4 c. chicken broth
1 lb skinless, boneless chicken breasts
1 medium onion, chopped
2 tbsp. olive oil
1 garlic clove, minced
4 medium carrots, cut diagonally into 1/3" slices
2 celery ribs, cut diagonally into 1/3" slices
1 tsp salt
1/4 tsp black pepper
3 tbsp fresh parsley
Bring broth to a simmer in a 2-3 qt. saucepan. Add chicken and simmer, uncovered, 6 minutes. Remove pan from heat and cover, then let stand until chicken is cooked through, about 15 minutes. Transfer chicken to plate and cool 10 minutes. Reserve liquid, uncovered.
While chicken is poaching, cook onion in oil in 4 qt heavy pot, covered, over moderate heat, stirring occasionally, until softened but not browned, about 6 minutes. Add garlic and cook, stirring, until fragrant, about 1 minute. Add carrots, celery, salt and pepper and cook, covered, stirring occasionally, until softened, 8-10 minutes. Remove from heat.
While vegetables are cooking, shred chicken into 1/4 inch wide strips. When vegetables are done simmering, stir chicken into soup along with parsley.