Heat a Dutch Oven or heavy bottomed soup pot over medium-high heat. Then add the butter, onion, and celery. Cook, stirring occasionally, about 5 minutes to soften.
Add the carrots and cook for 3 minutes, stirring occasionally.
Add the minced garlic, chicken, salt, and black pepper. Cook about 5 minutes, until the outside of the chicken is no longer pink (if using pre-cooked chicken, you will add that later).
Add the garlic powder, onion powder, sage, and rosemary. Stir well.
Stir in the flour and cook a minute or so, stirring constantly.
Stir in the chicken broth.
Add the potatoes and bring to a simmer. Lower the heat to medium-low and cover the pot, leaving the lid ajar. Simmer until the potatoes are fork-tender.
Add the frozen mixed vegetables (here is where you add pre-cooked chicken, if using), heavy cream, and the parsley. Stir well, then bring to a simmer again and cook for 5 more minutes.
Taste and adjust seasoning, if needed.
Serve hot with crusty bread or a green salad.