Onion Dip with Caramelized Onions

Slice the onions in half from tip to root and then peel away the brown dry layers. Slice the halves into ¼-inch slices and then cut those slices in half again.
Heat oil in a large frying pan over medium heat. Add the onions and salt and stir everything together to coat the onions evenly with oil.
Continue to cook, caramelizing the onions until deeply browned. Stir often and modulate the heat, if needed, to prevent burning. Add water, a tablespoon at a time, if the onions begin to stick.
Once onions are deep brown, jammy, and soft, add the soy sauce and balsamic vinegar and cook for 30 seconds, deglazing the pan.
Remove the onions from the heat.
In a medium bowl, combine the mayonnaise, sour cream, and pepper. Add the onions to the mayonnaise mixture and stir well to combine.
Chill the dip, covered, for 30 minutes or more to allow the flavors to blend.
Transfer the chilled dip to a serving dish and garnish with chopped herbs. Serve with potato chips, veggie sticks, or baguette slices.