Chop up two or three onions, depending on how gravy-greedy you are, and fry them in a saucepan with a little oil. It doesn't matter what your knife skills are like because these bits of onion are going to get blasted by your stick mixer or food process/blender anyway so it's really no biggie unless you're trying to impress someone while you're cooking ;-)
Once the onions are about two thirds cooked (bearing in mind you're going to cook them until they are almost caramelised, add a handful of diced mushrooms (optional, it is fine with just the onions), any kind will do, even the dried ones that you soak to re constitute add great flavour - make sure you keep the soaking water to add later too!
Next, pop it back on the heat and thicken with a little corn flour (mix about two teaspoons in some water and then slowly add to the mix while stirring until it thickens to the desired texture, you can add more liquid or more flour depending on the consistency you are after. Season to taste with either more soy sauce or salt and pepper and even a little tomato sauce (following Paul Kelly's advice) for sweetness and that extra tang ;-)
Enjoy it over your favourite roast veggies or with our delicious vegan meatloaf roast.