Melt butter in sauce pan with olive oil.
Add in the onions, salt, cayenne and black pepper. Saute at medium heat for about 10 minutes until softened and slightly golden in color.
Reduce heat to medium-low heat and continue to cook for 10 minutes, stirring frequently.
Add a pinch of sugar to help with the carmelization and continue to cook and stir for 10 more minutes. The result should be a darker color showing the final carmelization. Remove pan from heat and allow the onions to cool.
Place the cream cheese, mayo and sour cream in a mixer with paddle attachment. Blend together with the onions until smooth, scraping bowl at halfway point.
Serve at room temperature and store any unused portion promptly in the refrigerator.