I cook at home fairly often nowadays, but I have to admit that my food is only occasionally as good as the restaurant variety. I don't know what I'm doing wrong. I use fancy cookbooks, and I try to follow the directions. Not only that, but I use fresh, or fairly fresh ingredients. Even so, the restaurants beat me almost every time. Why?
So far as I can tell the difference is that restaurants use lard, butter, sugar and MSG, even when they say they don't. I could be wrong about that, but really...if it's not that, then what could it be? Sure, restaurants have professional cooks...but, doggone it...I have the books, and the books are written by professionals! What gives?
I decided to research the question by taking one of the recipes I make and going on the net with the question: "How come my Cashew Chicken doesn't taste as good as what I get in Chinese Restaurants?" Half the responses were insults like, "Because they're professionals, stupid!" but some of the answers were pretty interesting. They did a lot to explain why you can't learn everything from a cookbook.
Secondly, they use a lot of heat when they stir fry, more heat then most people like to use at home. Not only that, but they use peanut oil, which you probably don't use for health reasons.
Third, they use Chinese vegetables rather than Western substitutions. That includes the type of mushrooms that are appropriate for the dish they're making. They also use shallots instead of onions.
Fourth, they use "Chicken powder." Can you imagine that...CHICKEN POWDER!!! I had no idea there was such a thing. Restaurants use real chicken too, but they supplement it with chicken stock in powdered form. It's not the same as bouillon. You can get it at Chinese markets.
I wonder if the best Chinese restaurants use homemade stock? Stock is one of the secrets of classic French cooking. There's all kinds of stock...even mushroom stock!
Fifth: they steam vegetables using "court" bullion instead of plain water. It consists of water, spices like pepper and garlic, and an acidic ingredient like lemon juice, vinegar or wine.
Lastly, they use ingredients not mentioned in cookbooks, like fresh ginger juice, brown sugar, honey, fat or lard, MSG, and lots of salt.
The reason you don't see some of these ingredients in cookbooks is that modern readers won't buy books with recipes that contain things like lard and MSG. Our era regards food as medicine. Taste isn't primary. The poor restaurateurs are forced to give lip service to that, but to stay in business they have no choice but to add these ingredients on the sly, because the food simply doesn't taste as good without them.
Well, that's what the people on the internet are saying, at any rate. I haven't tried some of these ingredients yet, so I'm in no position to judge.