01 - Melt butter in a large skillet over medium heat. Add chopped onions, salt, pepper, and sugar. Cook stirring frequently until onions are golden brown and caramelized, about 18-20 minutes. Remove from heat and let cool to room temperature.
02 - In a medium bowl, combine mayonnaise, sour cream, softened cream cheese, Worcestershire sauce, and chopped chives. Mix thoroughly until completely smooth and creamy.
03 - Add the cooled caramelized onions to the cream base. Stir well to evenly distribute onions throughout the dip. Taste and adjust seasoning with additional salt and pepper if desired.
04 - Cover the bowl and refrigerate for at least 1 hour to allow flavors to meld and the dip to thicken slightly. The dip can be made up to 2 days in advance and stored covered in the refrigerator.
05 - Transfer the chilled onion dip to a serving bowl. Garnish with additional fresh chives. Serve alongside thick-cut potato chips for dipping.