Dice the onion into 1/2-inch pieces, dice the celery stalks and carrots, and set all vegetables aside. Pat the chicken breasts and thighs dry with paper towels, then season them generously on all sides with salt and black pepper. This drying step helps the chicken cook more evenly in the slow cooker.

Add the diced onion, celery, and carrots to the crockpot, then layer the seasoned chicken breasts and thighs on top of the vegetables. Pour in the 4 cups of water—it should cover the vegetables and reach about halfway up the chicken. Add the bay leaf, herbes de Provence, and apple cider vinegar, stirring gently to distribute the seasonings throughout the broth. The vinegar adds subtle brightness that deepens the overall flavor of the soup.

Cover the crockpot and cook on low for 6 to 8 hours. The long, gentle cooking time allows the chicken to become incredibly tender while the vegetables break down slightly and infuse the broth with their flavors. I prefer the longer cooking time (8 hours) when I have the time—it creates a richer, more developed broth.

Using tongs or a slotted spoon, carefully remove the cooked chicken pieces from the crockpot and place them on a cutting board or shallow dish to cool for 5-10 minutes until they're cool enough to handle. Once cooled slightly, remove and discard the skin and bones, then shred the meat into bite-sized pieces using two forks or your fingers.

Return the shredded chicken to the crockpot and stir well to distribute it evenly throughout the soup. Taste the broth and adjust seasoning as needed—you may want to add a bit more salt, pepper, or herbes de Provence depending on your preference. I like to add just a touch more herbes de Provence at this stage to brighten the flavor after the long cooking time.

If the soup has cooled significantly during the chicken processing, turn the crockpot to high for 15-20 minutes to warm it through, then ladle into bowls and serve immediately. The soup is now ready to enjoy as a comforting, hearty meal.