I make green and red curry a lot, and I agree that “jacking up” Mae Ploy will produce something as good as what you get in most restaurants. I’ve done it from scratch, which isn’t an issue because of the ingredients, as I live in East Hollywood, aka Thai Town. It’s more an issue because of the time it takes to pound everything in the mortar and pestle (or even with a food processor).
I’ve gotten the best results by picking up the following practices over time:
[ul]
[li]Use fresh kha (galanga)–but you don’t have to mince it, which is a lot of trouble. Just cut it in long, thin slices, and allow sufficient time to simmer the curry.[/li]
[li]Lemon grass is good, but keep in mind that it isn’t the lemon grass which imparts the “lemony” flavor, but rather the lime. (The lemon grass is just for a subtle aroma.) So really, the lime is more important than the lemon grass. If you make a big batch, you can hold the lime during cooking, instead adding it whenever you reheat a serving. Otherwise, it does doesn’t keep well with the coconut milk over time. And instead of kaffir lime leaves, you can use the peel from limes.[/li]
[li]If you make red curry, it’s extremely important to get the freshest Thai basil you can.[/li]
[li]You really must use fish sauce to salt the curry. Anything else just won’t work.[/li][/ul]
As for adding sugar, sometimes it’s just a little, to bring out certain flavors, the same way salt does. [ETA: What TriPolar says above.] But there are some dishes–such as pad prik king, which is a particular way to make red curry–where the sweetness of the (palm) sugar, in contrast with the spiciness, is a major characteristic of the overall flavor.
When I first moved here I found in one of the Thai markets this great cookbook, which was published by ASEAN and written for the Thai women who married American service members during the Vietnam war and suddenly were whisked away to the U.S. before their mothers could teach them to cook. (For this reason, I guess, the English side of the pages isn’t very carefully translated, but the important information in English is understandable.) The book kind of disappeared, but now with Amazon you can get it again.
If you really want to cook Thai food, I strongly suggest this book (it has two volumes). It emphasizes the underlying principles for cooking Thai food. There are all kinds of recipes online, but they’re mostly pretty wimpy on the strong flavors, which are what you probably like when you go to a Thai restaurant. And if any Thai curry recipe tells you to use soy sauce (instead of fish sauce), you might as well throw it away.