Heat large saute pan over medium heat. Slice onions into thin slices.
Add oil to the pan, then add onions and a sprinkle of salt.
Saute, occasionally stirring with a wooden spoon, until onions begin to brown on the bottom and soften (if onions look like they're starting to burn, quickly reduce heat to low).
After 8-10 minutes, add a little more salt, some pepper, and the wine if using. Reduce heat to low or medium-low and cook an additional ~10 minutes or until onions are extremely soft and browned, and liquid has been absorbed. If using vinegar instead of wine, add the vinegar at the end, so it only cooks for 2-3 min.
Recipe by Eating Made Easy at https://eating-made-easy.com/caramelized-onions-made-easy/