Combine potatoes, leeks, celery, broth, butter, garlic, bay leaves, thyme, salt and pepper in a 6-quart slow cooker; stir well. Cover and cook until the potatoes are tender, about 4 hours on High or 9 hours on Low.
Remove and discard the bay leaves. Stir in cream and Boursin. Cover and cook on High until the cheese has melted, about 20 minutes. Using a potato masher, mash the mixture to reach desired consistency.
Divide the soup among 8 shallow bowls. Top each with 1 ½ tablespoons crumbled croutons, ¾ teaspoon chives and ¾ teaspoon dill.
