1/2 Cup plus 2 Tbsp Extra Virgin Olive Oil
1 small Vidalia or other sweet onion, thinly sliced
1/4 Cup dry Sherry
1 tsp Dijon mustard
2 Tbsp Sherry Vinegar
2 Tbsp chopped oil-packed sundried tomatoes
1 tsp Thyme
freshly ground Black Pepper
Heat 2 Tbsp of the oil in a large skillet over medium-high heat. Add the onion and 3/4 tsp slat, reduce the heat to medium and cook, stirring, until starting to soften 2 to 3 minutes. Sprinkle with the sugar and cook, stirring, until completely softened and golden-brown, 10 to 15 minutes more. Remove the pan from the heat, add the sherry , and carefully return the pan to the stove,. Raise the heat to medium high and cook, stirring until the sherry has almost evaporated, about 1 minute. Transfer the onions to a cutting board, let cool for a couple of minutes and then chop.
In a blender, puree about 1/4 cup of the onions with the vinegar and mustard. With the motor running, slowly drizzle in the remaining 1/2 cup olive oil; the mixture will thicken. Transfer to a medium bowl. Stir in the remaining onions, sun-dried tomatoes, thyme, and salt and pepper to taste.