Preheat the oven to 350°F and grease a 9x13-inch baking dish. In a large skillet, melt the butter over medium heat. Add the chopped onions, celery, and minced garlic. Sauté for 5-7 minutes. Stir in the dried sage and thyme, and season with salt and pepper to taste. In a large mixing bowl, combine the granola and the sautéed vegetable mixture. Mix everything together until well combined. Gradually pour in the chicken or vegetable broth. Transfer the mixture to the prepared baking dish and spread out evenly. Cover the baking dish with aluminum foil and bake in the preheated oven for 30-35 minutes. This will allow the flavors to meld and the granola to absorb some of the moisture. After 30-35 minutes, remove the foil and continue baking for an additional 10-15 minutes, or until the top is golden brown and crispy. Once the stuffing is golden and crispy, remove from oven and serve.