Cut or rip the stale bread into cubes, and by handfuls drop the cubed bread pieces into the blender until you have coarse breadcrumbs.
Transfer the breadcrumbs to a large bowl. Set aside.
Saute the chopped onion and celery in the 2 Tbsp butter over medium heat until fragrant. Add this mixture to the coarse breadcrumbs and stir well.
Add the chopped parsley to the bowl. Stir to combine. Add the beaten egg/milk mixture and stir to combine.
Melt the 1/4 cup of butter in a saucepan and pour over the breadcrumb mixture. Stir to combine.
Add the poultry seasoning, 1 Tbsp at a time, stir to combine after adding each tablespoon. The stuffing should be fairly fragrant of poultry seasoning, onion and celery. (You may want more or less of the poultry seasoning, adjust to your liking.)
Season with the sea salt and pepper. Stir to combine.
Using your hands-stuff into the cavity of the turkey.