Caramelize the Onions: Heat olive oil in a skillet over medium heat. Add onions and cook for 30-40 minutes, stirring occasionally, until golden. Add sugar (if using) and garlic in the last 2 minutes. Let cool.
Prepare the Dip: In a bowl, mix sour cream, cream cheese, mayonnaise, Worcestershire sauce, and shredded cheese. Fold in caramelized onions, reserving some for garnish.
Bake or Chill: For a warm dip, bake at 375°F (190°C) for 20-25 minutes. For a cold dip, refrigerate for 1 hour.
Garnish and Serve: Top with reserved onions and fresh herbs. Serve with chips, crackers, or veggies.