Put the onions in a casserole and microwave on HIGH for 6 minutes.
Add the potatoes to the casserole with 1/4 cup (3 tablespoons) of water.
Cover and microwave on HIGH for 14 minutes.
Drain the vegetables and puree in a food processor, gradually adding the sour cream (creme fraiche), the whole eggs, egg yolk, grated nutmeg, curry powder, salt and pepper.
Puree until smooth.
Butter the base of a 1 1/2 quart (1.5 litre/2 3/4 pint) pyrex cake mold (mould).
Spoon in half the potato mixture.
Form the sausage meat into a roll the same length as the terrine, stick the pistachio nuts into it at regular intervals and put it in the terrine.
Cover with the remaining potato mixture.
Do not cover the mold (mould).
Put in the oven and micro wave on HIGH for 20 minutes.
Leave the pate to cool, then turn out on to a platter.