Heat 1 tbsp olive-oil medium-high heat in a large skillet. Add chopped onions & cook on high-heat for approximately 10 mins, constantly stirring with the spatula.
The onions should begin to brown, but without burning.
Reduce heat to medium & continue cooking onions for 10 mins, continuing to stir, as onions-brown much more without burning. At this stage add a pinch of salt.
Continue cooking for 10 mins on medium or low-heat, stirring occasionally to make certain onions do not stick to the base of the pan or burnoff.
In general, you need to consume cooked onions for 30 mins.
Remove the skillet from heat & sprinkle onions with a little amount of balsamic-vinegar to deglaze the pan.
With a spatula, stir the onions, then scratching the base of the pan and then coat onions with a pinch of balsamic-vinegar that you added. Remove onions to a plate.