Note: For an even thicker gravy, mix 1 tablespoon cornstarch with 2 tablespoons water and pour it in to the gravy.
In a small nonstick skillet, whisk the nutritional yeast and flour together and toast over medium heat until it smells toasty, about 4 minutes. Transfer to a medium-sized saucepan and whisk in the vegetable broth, soy sauce, onion powder, and garlic powder. Bring to a boil and let thicken as desired. Season with salt and pepper, to taste.