A while ago I was attempting to cook a curry.
The early stage involved frying some onions
until they were damn near dry, and a dark brown
colour (like french polished mahogany).

This worked OK, and the flavour was most
distinctive.

However...

The (Meyer) non stick pan ended up with a tightly
bonded thin (say 0.3 - 0.5 mm) layer
of black "stuff", which was not easily removable.
I tried soaking the pan (for 2 days) and boiling water
in it, but the stuff wouldn't come off.

I threw the pan out.

Recently, I did the recipe again, using a different
cast aluminium frying pan. I fried around 1Lb of finely
sliced onions, using around 10ml of oil.

Same result :-(

Although this time I eventually
managed to clean the pan, probably damaging the non stick
in the process, since the cleaning was rather "physical".

Am I doing something wrong, either in the cooking
or cleaning process?

Do others have good answers? I'd rather not increase
the amount of oil for health reasons, given the choice.

BugBeasr