In a large heavy bottomed pot, sauté onions with butter on medium high heat until softened and slightly translucent, about 3-5 minutes.
Add garlic and half of the salt, stirring until fragrant, about 30-60 seconds.
Add celery, onions, carrots and remaining salt to pot, Stirring for about 60 seconds.
Add chicken breast to pot and pour chicken broth. Bring to a boil, then cover and reduce to a rolling simmer for 15 minutes or until chicken is cooked and reaches an internal temperature of 165°.
Remove chicken breast and shred then add back to pot with 1/2 cup of water and dry pasta. Bring back to a boil and cook for 7-8 minutes until pasta is tender.
Reduce heat to low, add milk, lemon juice and zest, Herbs de Provence and pepper. Stir until well combined then serve.