Heat olive oil in a large stockpot over medium-high heat. Add the chicken cubes and sear until browned and internal temperature reaches 165 degrees Fahrenheit. Remove chicken and set aside.
In the same pot, add the diced onion, carrots, and celery. Sauté for 5-7 minutes until the onions are translucent and the vegetables have softened.
Incorporate the minced garlic and cook for 60 seconds until aromatic.
Pour in the chicken broth, scraping the bottom of the pot to release any fond.
Add the cubed potatoes, dried thyme, salt, and black pepper. Bring the mixture to a rolling boil.
Reduce heat to medium-low, cover, and simmer for 15-20 minutes until the potatoes are tender when pierced with a fork.
Stir the cooked chicken back into the pot.
In a small bowl, whisk together cornstarch and cold water to form a smooth slurry.
Slowly stir the slurry and heavy cream into the soup. Maintain a simmer for 3-5 minutes until the liquid has reached the desired viscosity.
Adjust seasoning with additional salt and pepper if necessary. Garnish with chopped parsley prior to service.