====== Caramelized Onion and Shallot Dip ======

===== Ingredients =====

  * 2 pounds large yellow or white onions, thinly sliced
  * 2 large shallots, thinly sliced (about 6 ounces total)
  * 4 sprigs thyme
  * 1/4 cup olive oil
  * Kosher salt and freshly ground black pepper
  * 1 cup dry white wine
  * 2 tablespoons Sherry vinegar
  * 2 cups sour cream
  * 1/4 cup minced fresh chives
  * 1/4 cup plain whole-milk Greek yogurt
  * 2 teaspoons onion powder

===== Instructions =====


  - Preheat oven to 425°. 
  - Mix onions, shallots, thyme sprigs, and oil in a large roasting pan. Season with salt and pepper.
  - Roast onion mixture, stirring and scraping down sides of pan every 10 minutes, until mixture starts to break down and turn golden brown, 45–55 minutes.
  - Discard thyme sprigs. 
  - Add wine and vinegar; stir to scrape up any browned bits from bottom of pan. 
  - Return onion mixture to oven. Continue roasting, stirring occasionally, until deep golden brown and completely caramelized, about 15 minutes longer. 
  - Spread onion mixture out on a rimmed baking sheet to cool.
  - Transfer onion mixture to a work surface and mince. 
  - Transfer to a medium bowl. Stir in sour cream, chives, yogurt, and onion powder. Season with salt and pepper. 

===== Do Ahead =====

Dip can be made 3 days ahead. Cover; chill.