I adopted this recipe from Recipezaar and have since made the recipe. It's very good and the only change I made was using 1 teaspoon dried thyme, as I didn't have fresh in the garden. The original poster said this recipe was adapted from Michael Chiarello.
- Heat a saucepan over medium-high heat.
- When the pan is hot, add the olive and heat.
- When the oil is hot, add pancetta and saute, and caramelize for about 10 to 15 minutes.
- Stir onion into mixture, toss and saute for another 10 minutes, until the onion begins to brown.
- Add garlic, thyme, and cider vinegar, and remove from heat.
- Allow mixture to cool for about a 1/2 an hour.
- Place cooled mixture into bowl, add mayonnaise and sour cream.
- Season with black pepper, to taste.
- Serve over iceberg wedges.