Combine the chicken, potatoes, carrots, onion, celery, garlic, salt and black pepper, thyme, bay leaf, and chicken broth in a 5-6 quart slow cooker; Cover and cook on HIGH for 4 hours. Remove and discard bay leaf.
In a glass measuring cup, whisk together heavy cream and flour until smooth. Pour into the slow cooker, stirring to combine. Add frozen peas. Replace cover and continue cooking for an additional 30 minutes. Serve with warm buttered biscuits.