Carmalized Onion Dip
I made this dip last summer and it is so good - I could get in the bowl and just swim around in it! 
INGREDIENTS
2 large yellow onions
4 tablespoons unsalted butter
1/4 cup vegetable oil
1/4 teaspoon ground cayenne pepper
1 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
1 teaspoon Dijon mustard
1 teaspoon balsamic vinegar
4 ounces cream cheese, room temperature
1/2 cup sour cream
1/2 cup mayonnaise
METHOD
Cut the onions in half and then slice them into 1/8-inch-thick half-rounds. (Yielding about 3 cups of onions)
Heat the oil and the butter in a large sauté pan over medium high heat (it works better to NOT use a non-stick pan). Add the onions, cayenne, salt and pepper and sauté for 10 minutes. Reduce the heat to medium low and continue to cook for 40 more minutes, stirring occasionally (but not too often-the onions should start to stick to the pan) until the onions are browned and caramelized.
Add the Dijon mustard and balsamic vinegar and continue to cook for about 10 more minutes. Allow the onions to cool.
This is what you want the onions to look like. Note that they are really dark because of the balsamic vinegar.
In a large bowl combine the cream cheese, sour cream and the mayonnaise. Whisk until smooth. Add all of the onions, reserving about a tablespoon for garnish, into the cream cheese mixture. Stir to combine and mix well. Transfer to a serving dish and top with reserved onions. Refrigerate overnight to allow flavors to combine. Serve at room temperature with potato chips.
Makes 2 cups.
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