1. Prepare the Vegetables: Begin by finely dicing your carrots, celery, and onion. Aim for pieces that are roughly the same size to ensure even cooking and a pleasing texture in the finished soup. This step is crucial for building the flavor base.

2. Combine Ingredients in the Crockpot: Place the boneless, skinless chicken breasts at the bottom of your slow cooker. Evenly scatter the diced carrots, celery, and onion over the chicken.

3. Add Seasonings and Broth: Sprinkle the dried thyme, dried parsley, garlic powder, a good pinch of salt, and a generous grind of black pepper over the vegetables and chicken. Pour the chicken broth over all the ingredients, ensuring everything is submerged.

4. Slow Cook to Perfection: Cover the crockpot and cook on high for 3-4 hours, or on low for 6-8 hours. The chicken should be very tender and easily shreddable with a fork, and the vegetables should be soft.

5. Shred the Chicken: Once the cooking time is complete and the chicken is tender, carefully remove the chicken breasts from the slow cooker and place them on a cutting board. Using two forks, shred the chicken into bite-sized pieces. Return the shredded chicken to the crockpot.

6. Stir in the Rice: Add the uncooked white rice to the crockpot, stirring it gently into the soup. The rice will cook directly in the flavorful broth.

7. Continue Cooking with Rice: Re-cover the crockpot and continue cooking on high for another 20-30 minutes, or until the rice is tender and has absorbed some of the liquid, thickening the soup slightly. Keep an eye on it to prevent overcooking the rice.

8. Finish with Cream: Just before serving, stir in the heavy cream. Allow it to heat through for about 5-10 minutes on low, but do not bring the soup to a rolling boil after adding the cream, as it can curdle. Taste and adjust seasonings (salt and pepper) as needed. Garnish with fresh parsley or dill, if desired, and serve hot.