Add the chicken pieces, potatoes, diced celery, diced onion, minced garlic, and frozen mixed vegetables directly to the slow cooker pot and set aside.

In a large skillet over medium heat, melt the unsalted butter.

Sprinkle the flour evenly over the melted butter and whisk gently to create a smooth paste, known as a roux.

Slowly add 1 cup of chicken broth while whisking continuously to avoid lumps.

Gradually whisk in the remaining 2 cups of chicken broth. Increase the heat to medium-high and bring the mixture to a gentle simmer, whisking often until thickened (4 to 6 minutes).

Remove the skillet from heat and stir in the dried thyme, paprika, garlic powder, onion powder, salt, black pepper, and dried rosemary thoroughly to infuse flavor.

Pour the thickened and seasoned sauce over the ingredients in the slow cooker and gently toss to coat.

Cover the slow cooker and cook on low for 6 to 7 hours, or on high for 4 to 5 hours, until the chicken is fully cooked and vegetables are tender.

Remove the lid and allow the soup to stop simmering.

Stir in the heavy cream (or half-and-half) and adjust thickness with extra chicken broth if desired.

Season to taste with salt and pepper then ladle the soup into bowls.

Top with warm biscuits and garnish with chopped parsley or thyme leaves.