2) Reduce the heat to medium-low and cook, stirring occasionally, for 20 more minutes until the onions are browned and caramelized. Allow the onions to cool.
3) Place the cream cheese, sour cream and mayonnaise in the bowl of an electric mixer fitted with the paddle attachment and beat until smooth. Add the onions, reserving a small amount for the garnish, and mix well. Season to taste. Garnish with the reserved onions and serve at room temperature.