In a large pot, heat olive oil. Add onions, carrots, and celery. Saute over medium heat for about 5 minutes. Stir often.
Add garlic and continue cooking for another 2 minutes. Remove from pan and set aside.
In same pan, add butter and flour. Mix well together with a whisk. Cook over medium heat for 2 minutes.
Slowly add chicken broth, while whisking.
Heat until mixture begins to thicken.
Stir in milk, salt, pepper, sherry, thyme. and parsley.
Let simmer for 3-5 minutes over low heat. Do not boil.
Stir in chicken and peas and cooked vegetable mixture. Remove from heat.