Start by peeling and slicing your carrots, chopping your celery and onion, and dicing your potato. Mince the garlic cloves and set everything aside.
In your crock pot, layer the long grain brown rice, followed by the carrots, potato, celery, onion, and garlic. This layering helps with even cooking.
Sprinkle the black pepper, crushed red pepper flakes, and salt over the vegetables. Add the fresh thyme sprigs for that wonderful aromatic flavor.
Next, place the 1-inch pieces of chicken breast on top of the vegetables. This will ensure they cook thoroughly and stay juicy.
Carefully pour in the chicken broth, ensuring all ingredients are covered. If needed, you can add a bit more broth or water.
Cover your crock pot and set it on low for 6-8 hours or high for 4-6 hours. This slow cooking process will allow all the flavors to meld beautifully.
About 30 minutes before serving, mix the milk and cornstarch together until smooth. Stir this mixture into the soup to thicken it up and add creaminess.
Once the cooking time is up, give the soup a good stir, taste, and adjust seasoning if necessary. Serve hot, garnished with fresh herbs if desired.