In a large skillet, heat the olive oil and butter over medium heat. Add the sliced onions and sprinkle with salt and sugar. Stir to combine.
Cook the onions, stirring occasionally, for about 25-30 minutes or until they are deeply caramelized and golden brown. If they start to stick, lower the heat.
Once the onions are caramelized, remove them from the heat and let them cool slightly.
In a mixing bowl, combine the sour cream, cream cheese, Worcestershire sauce, garlic powder, and black pepper. Mix until smooth.
Fold in the cooled caramelized onions and chives (if using) until evenly distributed.
Transfer the dip to a serving bowl and refrigerate for at least 30 minutes to allow the flavors to meld.
Serve chilled with tortilla chips or vegetable sticks.