While cooking, particularly things that cook slowly on the hob, it smells really good while cooking but when finished it never seems to have as much flavour as I hoped.
Am I doing something wrong or does this happen to everyone?
There are two components to flavor: aroma and taste. The wonderful smells you get are the volatiles of the ingredients you have been cooking, and while they add a lot to dishes, aromas are just part of what makes food enjoyable. One also needs to worry about taste, and that may be the missing part. When I decided to improve my cooking three years ago I was mystified by flavors. I wanted to know how spices worked and how to use them better, but all the reading and experimenting did not help my cooking.
Then I learned the Remick Maxim (lower the temperature when possible) and the quality of what I made went up more than in the entire previous year. I then heard Thomas Keller speak about salting and things clicked. One has to get the salt, acid, and sweetness of the dish right or everything else amounts to nothing. Once I learned to pay attention to taste, spices became easier.
The next steps have been:
One thing that can never be overstated with slow cooking is the flavor of your liquid.
If you slow cook in plain old chicken broth, it'll taste little better than if you cooked in water. You need to flavor and reduce the liquid before you add the meat, in order to maximize your flavors. Broth, wine, garlic, herbs, onions, carrots, etc, and cook it down before you add the meat, so that the meat can bubble happily in a bath of flavor.
And for gods sake, never add water. You have an opportunity to add something, so add something tasty.
I had the same experience for years. You're not doing anything wrong. It is generally in the nature of flavourings (spices, herbs, even vegetables) to release a shock of scent when they hit the heat, which is where the smell comes from.
Also, particularly with slow-cooking dishes like casseroles, rich thick sauces or things like dahls and curries the flavour when you turn the heat off isn't as good as you think it should be. The trick with these things is to remember that the chemistry is still going on even after the cooking is done.
I find, particularly with slow cooking dishes, that they tend to taste better the next day. In fact, these days I make Indian style dishes before going to bed, and then pack them for lunch the next day.
Remember that the flavour of your dish is going to depend on how diluted or concentrated the flavour actually is.
To make a stock based liquid more concentrated, you can reduce it (by simmering quickly). This allows water to evaporate as steam, which creates a stronger flavour.
Alternatively - sometimes you need to add more seasoning. It's a good idea to taste your food regularly as you cook, so you can make judgements about the correct ratios (and adjust as necessary).
With many recipes, starting with a good stock (or bouillon) is a very good way of ensuring that your dish starts off in a flavoursome way. I'd recommend doing some research in this area.
This sometimes happens to me, but I've learned some good ways to avoid it: