Preheat the oven to 350°F. Lightly grease a 9-by-13-inch casserole dish.
Preheat a 6-quart pot over medium heat. Heat ¼ cup of the oil, then sauté the onion, celery, and carrot with a pinch of salt until the carrot is softened and the onion is lightly browned, about 10 minutes. Stir in the onion powder, sage, thyme, remaining 2 teaspoons salt, and a few grinds of black pepper.
Transfer the vegetables to a large mixing bowl. Add the bread cubes and toss to thoroughly coat. Add the vegetable broth ½ cup at a time, stirring well in between additions of broth. The bread should be moist but not soggy, so make sure everything is not completely soaked through.
Transfer the stuffing mixture to the prepared casserole dish. Cover with aluminum foil and bake for 20 minutes. Uncover and bake until the cubes are nicely browned, about 10 minutes more. Let cool a bit before serving.
Notes
The best bread for this stuffing is a nice, big loaf of country white bread that you dice yourself. Sliced sandwich bread tends to be sliced too thin. It’s also best if the bread is a few days old and relatively dry. If it seems fresh and springy, toast the bread cubes for 5 minutes in a 325°F oven before proceeding with the recipe.
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