Vegetarian gravy - Good Food Middle East

Ingredients

• 1 onion, chopped
• 2 carrots, finely diced
• 2 celery sticks, finely chopped
• 2 bay leaves
• 1 large thyme sprig
• large knob of butter
• 1 tbsp sugar
• 2 tbsp plain flour
• 1 tsp Marmite (optional, but it does add colour and depth)
• 1 tbsp tomato purée
• 2 tbsp red wine vinegar
• 1l vegetable stock (or chicken or beef stock, if you prefer)
• soy sauce, to taste