Place chicken thighs in the bottom of a 6-quart slow cooker. Top with diced onion, carrots, celery, potatoes, and minced garlic. Pour in the chicken broth and sprinkle with thyme, rosemary, salt, and pepper. Add the bay leaf and stir gently to combine.

Cover and cook on LOW for 6-8 hours or on HIGH for 3-4 hours, until the chicken is tender and cooked through.

Remove the chicken from the slow cooker to a plate or cutting board. Use two forks to shred the chicken, then return it to the slow cooker. Remove and discard the bay leaf.

In a small saucepan over medium heat, melt the butter. Whisk in the flour and cook, stirring constantly, for 1 minute. Gradually whisk in 1 cup of the hot broth from the slow cooker until the mixture is completely smooth.

Pour the roux mixture back into the slow cooker and stir to combine. Stir in the heavy cream and frozen peas. Cover and cook on HIGH for 15-20 minutes, or until the stew has thickened. Stir in the chopped fresh parsley just before serving.