Melt butter in a skillet over medium heat. Sauté onion, celery, parsley, and mushrooms in butter for approximately 10 minutes, until onions are translucent.
In the slow cooker, combine bread cubes, vegetables, and the seasoning package (included with the stuffing mix).
Pour in broth.
Mix in eggs.
Cook on high for 45 minutes.
Stir gently. Reduce heat to low, and cook for 4 hours.
If the stuffing is ready before the turkey, reduce heat to warm until ready to serve.