2 cartons natural yogurt
1 large onion
About 8 oz mushrooms - field mushrooms are fine, or shii take, or a
mixture.

Make yogurt cheese by draining the yogurt through a hanky for 24
hours in the fridge.  Next day, chop onion and saute in a little water.
Add mushrooms, which will eventually give off some liquid - simmer until
this has evaporated, stirring all the time.

Season to taste, then place in food processor, add yogurt cheese, and blend.
You could use low-fat cream cheese, if you preferred, or drained fromage
frais.  My mother would add about 2 tsp melted butter to this, to make
it set, but I didn't bother - it is quite spreadable as it is.  Keep in
the fridge.

My mother makes an infinite variety of pates with low-fat cream cheese
as a base - trout (she adds a squirt of tomato paste for colour), 
pheasant, liver, you name it - she basically adds whatever the main 
ingredient is to cream cheese - obviously if it's meat or fish it has
already been cooked in some way - processes it, seasons to taste, and she
always adds melted butter to help it set, but you really don't have to,
if you don't mind it a little runny.