– Peel and slice onions. Melt butter in a large skillet over medium-high heat. Add onions and stir to coat in butter. Cook for 5 minutes. Reduce heat to medium-low, cover the skillet and cook for 10 to 15 minutes until caramelized. Remove from heat.
– Add sour cream, mayo, garlic, salt, pepper, and onions to a food processor.