In a saucepan, sauté the onion with the olive oil and brown sugar, until light golden brown.
Add the diced mushrooms and cook down until the mushrooms have shrunk down and their liquid has cooked off.
Stir in the dried herbs, balsamic vinegar and flour until well combined.
Next, add the soy sauce and vegetable stock. To make the veggie stock we use 1½tsp bouillon mixed with 1½ cups boiling water.
Simmer the gravy until it reaches your preferred thickness. We let it simmer for around 5 minutes for a quite thick gravy.
Pour into a jug or gravy boat for serving, and season with salt and pepper to taste.
You can also use cornstarch to thicken the gravy instead of flour. Use 1 tbsp cornstarch (or half the amount of flour if you are making more than the standard recipe) and mix it with 1 tbsp water into a smooth slurry. Whisk the slurry in when you add the vegetable stock and bring up to a simmer and stir whilst it thickens.