In the slow cooker, add chicken thighs, potatoes, carrots, celery, onion, and garlic.
Pour in the chicken broth, ensuring all ingredients are covered.
Add thyme, rosemary, bay leaf, salt, and pepper. Stir gently to combine.
Cover the slow cooker and cook on low for 6-8 hours, or on high for 3-4 hours, until the chicken and vegetables are tender.
About 30 minutes before serving, remove the bay leaf and stir in the frozen peas.
In a small bowl, whisk together flour and a little water to create a paste, then stir this into the stew to thicken the broth.
Continue to cook on high for an additional 30 minutes.
Before serving, taste and adjust seasoning as needed, garnishing with fresh parsley if desired.