Finely dice onion.

Caramelize onion in butter until golden to dark brown.

Mix together in a bowl, mayo, sour cream, onion powder, celery salt, garlic powder, and white pepper

After onion is caramelized, put them in a bowl and let them cool either on the counter or in the fridge.

Mix together the cooled onions and sour cream mixture.

Let dip cool in the fridge for at least one hour prior to serving.