Add in the onions and celery and cook stirring until soft and translucent but not browned (about 6 minutes).
Add in the garlic and cook for 2 minutes.
Add in chopped mushrooms, creamed corn, niblets corn, broth, poultry seasoning, parsley, Parmesan cheese, seasoned salt or white salt and black pepper pepper; bring to a medium boil, simmer for 10-15 minutes over low heat.
Remove the mixture and transfer to a large bowl; and cool for 20-30 minutes (cool just enough so that the eggs will not cook when added).
Add in eggs and mix well.
Add bread crumbs or cubes; mix well to combine (I use my hands for mixing).
Taste the mixture and then adjust the poultry seasoning, salt and pepper to taste if needed.
At this point you may cover the bowl and refrigerate until ready to shape into balls.
With moistened hands shape into golf ball-size balls (I use an ice cream scoop for this) add in more breadcrumbs if needed just to hold the mixture together.
Transfer the shaped balls to the prepared buttered casserole dish (at this point they can be covered and refrigerated until ready to bake).
When ready to bake drizzle melted butter over the balls.
Cover loosely with foil.
Bake at 350°F for about 20-25 minutes (do not overbake).