Preheat oven to 350°F (175°C). Grease a baking dish with butter.
Spread the bread cubes on a baking sheet and toast in the oven until lightly golden, about 10 minutes. Set aside.
In a large skillet, melt butter over medium heat. Add leeks and celery; cook, stirring, until soft, about 10 minutes.
Add sage and parsley, and cook for another 2 minutes.
In a large bowl, combine the bread cubes, leek mixture, and chicken broth. Season with salt and pepper.
Transfer the mixture to the prepared baking dish. Cover with foil and bake for 25 minutes. Remove the foil and bake until the top is golden and crisp, another 10 minutes.
Serve hot alongside your favorite holiday dishes.