Preheat oven to 300°F. Place bread cubes on a baking sheet and toast 10-15 minutes, just until lightly crunchy. Allow to cool slightly before placing in a large mixing bowl and set aside.
Increase oven temperature to 350°F.
Heat butter in a large skillet over medium-high heat. Add cubed chicken, onion, celery, salt, pepper, and thyme. Cook, stirring frequently, 10-12 minutes, until vegetables are tender. Stir in the apples and sage, then continue cooking an additional 1-2 minutes. Pour over the bread cubes.
Stir in the vegetable broth and mix gently to get everything evenly distributed and coated with the broth. Season with salt and pepper, to taste.
Pour stuffing into a prepared 8x8 glass baking dish. Bake 45-50 minutes, until lightly browned on top. Serve warm or room temperature.