This recipe comes from Rose Elliot's Vegetarian Cookery and is excellent.
1 onion, diced
As a variation, try adding a diced red pepper, a handful of cashew nuts, about 8 diced button mushrooms and a dash of red wine. Rather than straining the gravy, whizz it in a blender. Yum!
Fry the onion in the oil for 5 mins.
Add the flour and cook for a further 5 to 10 mins until the flour and onion are nut-brown and the onion is soft and slightly pulpy.
Add the garlic then gradually stir in the vegetable stock (or the water from any vegetables you happen to be boiling at the same time). Bring to the boil and simmer for 10 mins.
Add the yeast extract, soya sauce and black pepper. Stir well. Strain if you like, or serve as it is.