Position rack in center of oven. Preheat oven to 350°F/180°C. Coat the inside of a 2 to 3 quart (2 L to 2.8 L) ceramic casserole dish with nonstick spray; set aside.

Cut the bread into small cubes and scatter in a single layer on a rimmed half-sheet baking pan. Toast the bread in the oven for about 8 minutes, tossing once during baking time, to begin to dry out the surface of the bread a bit; it will not color. Cool completely and scrape into large mixing bowl.

Meanwhile, slip the pork sausage out of its casing into a large sauté pan, break up the sausage meat, and cook over medium heat, stirring often, until no longer pink. Transfer to the bowl with the bread, draining away and discarding any fat.

Place sauté pan back on stovetop, add butter and melt over low-medium heat. Add celery, leeks and scallions and sauté for a few minutes or until softened but not browned. Add the chopped apple, parsley, sage, thyme, salt and pepper and sauté for about 1 minute more to combine. Turn heat up, add the white wine and sauté for about 1 minute more. Scrape mixture over bread cubes and fold well to combine. Add enough stock to create a slightly moist mixture. Scrape into prepared dish and cover with aluminum foil.

Stuffing may be prepared up until this point, covered tightly with plastic wrap and refrigerated overnight. Bring to room temperature before baking.

Bake, covered with foil, for about 30 minutes, remove foil and continue baking until hot all the way through and a bit crusty on top. Serve immediately.