1. Peel the onions and slice them into thin 1/4-inch half-moons. Mince the garlic and chop the thyme leaves.

2. Set a large heavy skillet over medium-low heat and add the butter and olive oil. Once melted, add the sliced onions, 1/2 teaspoon of the kosher salt, and the sugar. Stir to coat the onions in the fat.

3. Cook the onions for 25 to 35 minutes, stirring every few minutes, until they become very soft, golden brown, and deeply caramelized. Adjust the heat as needed so they slowly brown without burning. If the pan gets dry, add a tablespoon of water and scrape up any browned bits.

4. Stir in the minced garlic and thyme and cook for 1 to 2 minutes more, just until fragrant. Remove the pan from the heat and let the mixture cool to room temperature.

5. In a medium mixing bowl, combine the softened cream cheese, sour cream, and mayonnaise. Beat or stir until smooth and creamy.

6. Add the Worcestershire sauce, lemon juice, remaining 1/2 teaspoon kosher salt, and the black pepper. Mix well and taste, adjusting seasoning as needed.

7. Fold the cooled caramelized onions into the creamy base until evenly distributed. Stir in the chopped chives, reserving a small handful for garnish.

8. Transfer the dip to a serving bowl, cover, and refrigerate for at least 1 hour and up to 24 hours to let the flavors meld and the dip firm up.

9. Before serving, let the dip sit at room temperature for about 15 minutes, then stir and garnish with additional chives and a little extra black pepper. Serve with chips, crackers, or fresh vegetables for dipping.