To the slow cooker, add chicken, potatoes, celery, onion, garlic, and the frozen vegetables. Set aside.

Make the sauce: In a large skillet over medium heat, melt the butter. Sprinkle the flour over the melted butter and whisk together gently to form a paste. Add 1 cup chicken broth. Whisk until smooth then add the remaining 2 cups of broth. Increase the heat to medium-high and bring to a simmer.

Continue to cook until slightly thickened, 4-6 minutes, whisking often. Remove the skillet from the heat, and stir in the thyme, paprika, garlic powder, onion powder, salt, pepper, and rosemary.

Pour the thick sauce mixture over the ingredients in the slow cooker. Using a spatula, gently toss everything together.

Cover and cook on the low setting for 6-7 hours or on the high setting for 4-5 hours.

Just before serving, remove the lid and allow the soup mixture to stop simmering. Stir in the cream. If desired, add additional broth to reach desired thinness/thickness. Adjust salt and pepper to taste.

Serve the soup in bowls. Garnish with fresh parsley or fresh thyme, if desired.