I have a technique with Patak's sauces that gets you something a bit closer to what you might get at a British Indian Restaurant. Basically you make effectively a base sauce - it's very similar to making a thin blended soup.
Take onions, garlic, carrots, sweat down in oil or ghee for until nice and soft.
Add some fresh chillis or chilli powder if you want a touch more heat.
Add the Patak's curry paste, about half the jar will make enough for curry for 3-4 people.
Fry off the paste for a few seconds. If it's a tomato based sauce add a tin of tomatoes here, if its a korma or say something with coconut milk then don't.
Add some water or some chicken stock. Not sure of the quantities - probably about 3/4 of pint (less if you have the tomatoes).
Bring to the boil and simmer for 10mins.
Let it cool and then blend in a blender or with a blending stick - you should get a thickish gravy.
You can freeze this if you want and be ready to make a quick curry.
For the curry, fry your meat and/or vegetables, add the base sauce and hey presto.
For a korma for example, fry some dessicated coconut and sugar in oil for a 30secs, add meat or veggies that you fried earlier, then the base sauce - bring to the boil and reduce until a nice thick consistency - add cream or coconut milk.