Melt butter in a skillet over medium heat and stir in poultry seasoning, salt, and pepper.
Add diced onions and celery; cook until softened, then let cool completely.
In a large bowl, combine bread cubes, parsley, and fresh herbs (if using).
Pour the cooled onion and celery mixture over the bread cubes and mix gently.
Gradually add chicken broth to moisten the bread cubes, then stir in beaten eggs.
Transfer the stuffing mixture to a greased slow cooker.
Cook on High for 30 minutes, then reduce to Low and cook for 3-4 hours.
Keep on the Warm setting if done before serving.