Heat the butter and oil over medium heat in a large pan. Add the onions, salt, and sugar. Cover pan and cook gently for about 10 minutes. Uncover, stir and reduce the heat to medium-low. Cook, stirring every several minutes and cook for about 20 to 25 more minutes until the onions are browned and caramelized. Allow to cool. May be made ahead and stored three or four days, covered, in the fridge.
Place the cream cheese in a mixing bowl, and using a paddle attachment, beat until smooth. On low, slowly mix in the sour cream and mayonnaise. Add the onions, pepper, and cayenne and mix well by hand until just mixed. Dip can get “sticky” if over mixed. Taste for seasonings, but keep in mind it takes a little time for the flavors to meld.
Serve at room temperature.
Keywords: Appetizer, Caramelized Onion, onion dip, onions, Sour cream, Spreads and Dips