In a large Dutch oven or pot, heat the butter over medium-low heat. Once melted, add the chopped onion, sliced carrots, and celery. Cook for 6 – 8 minutes, stirring occasionally until the vegetables are soft and wilted. In the last 30 seconds of cooking, add the minced garlic and stir well.

Sprinkle the flour over the cooked vegetables and mix thoroughly until coated. Let this mixture cook for an additional minute.

Gradually pour in the chicken stock and milk, stirring to combine. Add the sweet potatoes, salt, pepper, and thyme, then bring the mixture to a boil. Once boiling, reduce the heat and let simmer for 15 – 20 minutes, or until the potatoes are fork-tender.

Fold in the cooked shredded chicken, frozen peas, parsley, and optional spinach. Allow to simmer together for another 5 minutes.

Adjust seasoning as needed, remove from heat, and serve.