Here is the secret recipe. Actually, it is not really a secret as your neighbourhood Indian restaurant is probably preparing your Friday night feast with something very similar, but they have been making darn sure the customer is kept in the dark. Until now!
NB We have given the South Asian version. For an authentic South East Asian version, exchange the onions and ginger for shallots and galangal.
4-5 medium onions, peeled and quartered (800g approx unpeeled weight)
1 head garlic, peeled (i.e. lots of cloves!)
120g/4oz piece of ginger, chopped into small pieces (peel if you like - we don't bother: as with a lot of things, the flavour is in the skin!)
1 litre water
Place all the ingredients in a pan, bring to the boil and simmer until the onion is soft and translucent (about half an hour).
Leave to cool, then blend till smooth. You will have about 1.2 litres or a little more.
You can leave this sitting around on the stove-top for a day, then it will last for about a week in the fridge, so you can make it a couple of days before you start cooking the actual curries.
Our recipes use 300ml/half pint amounts of Secret Sauce, so the above makes enough for four. This can be frozen in recipe-sized portions to simplify future curry-making sessions. When defrosting you can just empty it straight in to the pan to let it melt, or let it sit around for a few hours in a bowl if you are organised enough!
We find that preparing the above in double or even triple batches in a very large pan makes life even easier. There is a wonderful rubber tube for peeling cloves of garlic that is available from all good cook shops, so you don’t even get smelly hands!
NB. You are very welcome to make a curry without using this technique! You can take the onion, garlic & ginger and blend to a paste. OR, chop an onion finely, fry gently in some oil and add a squirt each of garlic and ginger from a tube. In both cases at some stage in the cooking process add 200ml of water.