Chop the onion, melt the butter in a pan, and sauté the onion gently till transparent.
Add the mushrooms, and sauté until they begin to give off their juices. Grind the nuts in a grinder or food processor. Bring the stock to the boil, stir in the yeast extract and add all the other ingredients.
Stir well.
Turn into a greased baking dish and bake at 180 degrees Celsius/ 350 Fahrenheit/gas 4, for about 30 minutes.
Serve hot with tomato sauce. If you are going to eat it cold leave to cool in the tin, then turn out into a shallow dish. Cover with cling film and refrigerate. Serve with tomato sauce.