New England Stuffing

This is the only recipe MY MOTHER asked me to have and for a proud cook, that's a big deal! I love it! It's different and yet comforting and familiar.

1 pound hot Italian sausage, casings removed
1/4 cup unsalted butter
2 large onion, chopped
2 cups chopped celery, with leaves
1 (8 ounce) jar steamed or roasted chestnuts, chopped
1/4 cup chopped parsley
1 tablespoon poultry seasoning.
22 ounces oyster crackers, lightly crushed
1 1/2 cups chicken stock
1 egg

In a medium skillet, cook sausage until cooked through, crumbling as you cook. Transfer to a bowl. Add butter to the skillet and melt over medium heat. Add onions and celery. Saut