Melt unsalted butter in large frying pan over medium-low heat. Remember, slow and steady wins this race.
Add onions, salt and sugar, toss to coat lightly in melted butter. Now you wait. Continue heat at medium-low, toss every 5-10 minutes. If nothing is happened, increase heat slightly. If they are cooking too fast, reduce heat. So where is what to expect:
Onions will start to reduce. They are made mostly of water and as the water releases and evaporates, the onions will start to deflate and reduce in size.
At around 20 minutes in you will get your first hint of the "caramel" color you are seeking.
At 45 minutes you will have a nice brown batch of onions. Depending on your taste buds and how you intend to use them, you can stop at any point in time. Do a taste test first to make sure they are nice and sweet.
If you've tried this recipe, come back and let us know how it was!