Preheat oven to 350°F (175°C).
Roast butternut squash cubes on a baking sheet for 20–25 minutes until tender and golden.
In a skillet, melt butter over medium heat. Sauté onion, celery, and sage until softened, about 5–7 minutes.
In a large bowl, toss together bread cubes, roasted squash, sautéed vegetables, salt, and pepper.
Pour broth over mixture and gently stir until well combined.
Transfer to a greased baking dish and cover with foil.
Bake for 30 minutes covered, then uncover and bake an additional 10–15 minutes until top is golden.