In a large skillet, melt 1/4 stick (2 tablespoons) of the butter. Add the apple wedges and onions. Season with the sugar and salt and pepper to taste. Cook over medium heat until the apples and onions become slightly tender and yielding but still hold their shape, 5 to 8 minutes. Stir in the celery and cook to soften it slightly, about 2 additional minutes. Remove the skillet from the heat and transfer the contents to a bowl. Set aside.
Arrange the bread slices in a single layer on a baking sheet and toast until light brown. Alternatively, brown them in a toaster. While the bread is still hot, lightly butter both sides of each piece. Cut into 1-inch squares and transfer them to a large bowl. Toss with the rosemary, sage and some salt and pepper. Mix to blend. Set aside.
Heat a large skillet and add 1 tablespoon of the butter. When it melts, stir in the turnip cubes and sprinkle with the allspice. Season with salt and cook over medium heat until tender, 3 to 5 minutes.
Combine the apple, onion and celery mixture with the cooked breakfast sausage and turnips in the bowl containing the toasted bread. Mix to blend, and add the chicken stock to moisten all of the ingredients.
Place into a rectangular baking dish and bake until golden and cooked through, 45 to 50 minutes.