What you need:
1 Large Onion, sliced (Spanish works nicely but is slightly sweeter)
1 cup sliced mushrooms
Salt
1 tablespoon Olive oil 

Turn the heat to low and let the onions break down until it turns a nice golden colour. This takes a while approximately 30 to 40 minutes but don't try to speed up the process by turning the heat up otherwise the caramelization process won't occur and you'll end up with either burnt or raw onions. 

What to do:
In a sautee pan heat the olive oil and add your sliced onions. Add a pinch of salt (the salt helps the caramelization process happen faster but only if you add it as soon as the onions hits the heat). 

Turn the heat to low and let the onions break down until it turns a nice golden colour. This takes a while approximately 30 to 40 minutes but don't try to speed up the process by turning the heat up otherwise the caramelization process won't occur and you'll end up with either burnt or raw onions. 

Add the mushrooms and continue to sautee for another 5 to 8 minutes. Makes a fantastic topping for any sandwich, burger or steak. Or try it with my fried veal recipe!