This gravy is a basic "brown" gravy similar to what you get using a pouch of supermarket instant gravy.
The onion should be chopped finely, almost a mince. For this quantity of gravy, not too much is needed. Sautée the onion in the oil over medium heat with salt and pepper, until the onion begins to turn golden brown. Add the flour and stir. A roux should form, cook it for several minutes until it starts to darken.
Add the stock and stir until smooth. Add the yeast extract--as the gravy warms it will become incorporated. Taste and season if necessary. When the gravy simmers, it is done. Strain into a gravy boat or other serving container and allow to cool a few minutes before serving.
Makes about 1½ cups gravy.