Place the oil in a small saucepan over a medium-low heat. Add the flour and spices, and mix thoroughly to produce a fragrant paste. Cook for a minute or so, stirring constantly, then add the tomato puree, and cook for a further 1 minute.

Add the vegetable stock a little at a time (I usually add it about 1/3 at a time), mixing well until smooth each time before adding a bit more. When you've added all of the liquid, you should have a smooth, silky sauce.

Season with plenty of black pepper (you probably won't need any salt unless you used low-sodium stock), and use to make enchiladas (or something else!).