Heat 6 tablespoons of butter in a large saute pan over medium heat. Add the thinly sliced onions, cayenne, salt, and pepper and saute for 8-10 minutes.

Reduce the heat to medium-low and cook, stirring occasionally, for 15-20 more minutes until the onions are soft, browned and caramelized. Add additional butter as needed. Cool to room temperature.

Place the cream cheese, sour cream and mayonnaise in the bowl of an electric mixer and beat until smooth. Add the onions and mix well.

Add additional salt and pepper, to taste, if desired. Serve at room temperature.