Sugar in Indian curries?

There is nothing inauthentic about using sugar in an Indian dish, even a savory one. For example, Gujarati cooks often add raw sugar (jaggery) to daal and curries. Quoth Wikipedia:

"It is common to add a little sugar or jaggery to some of the sabzi/shaak and daal. The sweet flavour of these dishes is believed to neutralize the slightly salty taste of the water."

And here's an example Gujarati potato curry recipe, which includes a tablespoon of sugar.

As for how much to add, that's a matter of your taste and the level of acidity and/or saltiness in the dish. My Gujarati friends in Boston like stuff rather sweeter than I would personally prefer, so be cautious.

I have a restaurant in Delhi.

Whether you add sugar to a curry really depends on the region you're cooking is from.

A Kashmiri dish will usually never have sugar in it, but may have raisins or dates added if sweetness is required.

In contrast & (as previously mentioned) most savory Bengali dishes will have a bit of sugar added (my Kashmiri husband hates this).

It is also interesting to note that the type of onion most commonly used in India is a small pink/red onion that has quite a bit of sugar. That is where the caramelized 'sweetness' in many Indian dishes comes from.

And yes, it is quite an 'art' to get those tonnes of onions perfectly caramelized!

It depends on your ingredients, as you allude to, sugar can help balance some flavors. For example half a teaspoon of sugar can help counteract the acidity of tinned (crushed) tomatoes if you're using them in a curry.

yes, adding a little bit of sugar and lime juice always give it an extra flavor and freshness, specially if it is a heavily spiced curry.

I have a recipe book for cooking curries 'just like an Indian restaurant'. The most glaringly obvious point is that just about every curry (except cream-based ones like kormas) start off with tons of onions, sweated for hours.

This releases a lot of natural sugars from the onions, so most restaurant curry sauces do have an underlying sweetness. Obviously most home cooks don't have hours to spend sweating onions, so naturally their curries don't taste quite the same. Adding sugar recreates the sweetness somewhat. Their are other factors (like adding half a tin of ghee to every curry), but it does help and there's nothing wrong with it.

I find that sugar gets added to the curries from Malaysia, Singapore, Thailand etc sometimes.

They are usually sour and sweet, eg use tamarind and tart ingredients like lemongrass, or very salty smelly like blachan or fish sauce. these need leavening with sugar so follow the recipe for good results.

Adding sugar on the off chance I would be less certain of. A garnish of half a sliced onion, fried until brown, and added last, will typically work well, esp with lentil dhals as the caramel in the onions comes through

Adding sugar does not make large changes in taste of recipes, A small quantity of sugar can be added to make it tasteful.

The only use of sugar in a curry is for its color. It gives a brown tint to the dish and is always used in least amount.

If you put it for balancing spices then put a balanced amount of spices in the first place rather than balancing it later with sugar.

Given that Masala based curries always get some sweetness from tomatoes (which could be anything from sour to rather sweet), and it is generally a good idea to balance tomato based sauces of all kinds with sweet (sugar, jaggery)/sour (yoghurt, vinegar) ingredients at the end, how could one find fault with this?