Tips for caramelising onions:
Low heat.
Long time.
Don't mix too often.
Do a large quantity.
I'm doing about 2kg of onions right now, it's been going for about 3 hours, and I reckon it's got another 3 in it. At least.
You're basically sweating onions.
Turning the sweat into an "onion stew".
Then reducing that stew into thick, fibrous caramel.
This can be used as a base for the best onion soup you've had.
Similar to the onion tarts: add water until you have a soup, pour into bowls, add a round of baguette, liberally top in Gruyère, then grill/broil the top.
Almost the same ingredients, used slightly differently