Caramelized Onion Dip

My friend held her second annual wine tasting party tonight.  This year, in addition to bringing a bottle of wine, each attendant was asked to bring either an appetizer or a dessert.  I brought a bottle of gewürztraminer and this dip, which I found here on Pink Parsley, originally from Ina Garten.  I enjoyed this dip very much.  The cayenne gives it a little punch of heat and the caramelized onions are amazing!  It didn't see too many others eat it, which disappointed me a little bit since I rushed home from work to make it, but it left more for me to enjoy, since it was my dinner!

2 Vidalia or Yellow Onions (I only used 1)
3 tablespoons Butter
3 tablespoons Olive Oil
1/4 teaspoon Cayenne Pepper
1 teaspoon Salt
1/2 teaspoon Black Pepper
4 ounces Cream Cheese, at room temperature
1/2 cup Sour Cream
1/2 cup Mayonnaise

Cut the onions in half and slice them into 1/8-inch thick slices.  There should be about 3 cups total.  Heat the oil and butter in a large sauté pan over medium heat.  Add the onions, cayenne, salt, and pepper and sauté for 10 minutes.  Reduce the heat to medium-low and cook, stirring occasionally, for 20 more minutes, until the onions are browned and caramelized.  Allow to cool slightly.  In a bowl, combine the cream cheese, sour cream, and mayonnaise and beat with an electric mixer until smooth.  Add the onions and mix until well combined.  Taste for seasonings.  Serve immediately or chill to serve later.