Preheat oven to 350 degrees F.
Lightly butter a large rectangular baking pan.
Heat 2 tablespoons of the butter in a large skillet over medium-low heat. Saute onions and celery in the butter until tender; remove from heat an add a small pinch of cayenne and let cool.
Combine cornbread and breadcrumbs in a large bowl. Gently fold in sauteed onions, salt, pepper, and parsley.
Add beaten eggs and toss more; moisten with the reserved oyster liquid until moist but not soggy. Gently stir in the oysters.
Pat the mixture into the prepared baking pan (it should make a 1-inch layer in the pan).
Dot with remaining butter and bake about 45 minutes, until golden brown and set in the center.
Grandma's Oyster Dressing Recipe: https://whatscookingamerica.net/Seafood/OysterDressing.htm