Preheat oven to 375°F. Lightly grease a 2-quart casserole dish.

In a measuring cup, mix together the hot water and broth powder. In a large bowl, combine the bread cubes and hot broth mixture, tossing until the bread cubes are well coated. If using gluten-free bread, it will rehydrate right away. Set aside.

In a large skillet over medium high heat, add the oil and swirl to coat the bottom of the pan. Add the celery and onion and cook, stirring as needed, until tender, about 10 to 15 minutes. If the onion mixture is starting to stick and burn, add a couple of tablespoons of water, as needed.

Add the sautéed onion mixture to the bread cubes, along with the nutritional yeast flakes, sage, and marjoram. Add the ground white and black pepper to taste. Adjust seasonings, adding salt to taste if necessary.

Transfer the dressing mixture to the greased baking dish, cover with a lid or foil and bake in the preheated oven for 15 minutes. Uncover the dressing, drizzle with the melted margarine and return to the oven, uncovered. Bake the dressing for 35 to 45 minutes, or until the dressing is lightly browned and crispy on top. Serve hot.