Possibly relevant to the onion boiled flavour and and heat discussion:

When onions and their relatives are heated, the various sulfur compounds react with each other and with other substances to produce a range of characteristic flavor molecules. The cooking method, temperature and medium strongly affect the flavor balance. Baking, drying, and microwaving tend to generate trisulfides, the characteristic notes of overcooked cabbage. Cooking at high temperatures in fat produces more volatiles and a stronger flavor than do other techniques.

via http://cooking.stackexchange.com/questions/8289/why-do-onions-taste-sweeter-when-cooked-at-lower-temperature