Thinly slice the onions. In a large cast iron skillet, melt the butter over medium heat and add the onions. Toss the onions to coat and cook for about 10 minutes. Add in the salt and toss lightly. Continue to gently cook the onions for the next 30-45 minutes. Stir the onions every few minutes making sure that the skillet stays at a low enough heat that the onions don’t burn ( they will brown at the end of the cooking)
Once the onions are soft and caramelized you can add the vinegar to the pan to deglaze and add a little more flavor. Remove the onions from the pan and cool.
In a mixer, mix together the cream cheese, sour cream, Worcestershire, bacon, green onions, and seasonings. Add in half of the caramelized onions. Stir together and serve or keep refrigerated for a week.