Peel and slice the sweet onions thinly for even cooking.

In a skillet over medium heat, melt 2 tablespoons of butter. Add sliced onions and cook for about 20 minutes until golden brown, stirring occasionally.

Stir in minced garlic, salt, and pepper; cook for an additional 1-2 minutes.

In a bowl, mix sour cream and mayonnaise until smooth.

Fold in the cooled onion mixture gently until well combined.

Cover and refrigerate for at least 30 minutes to allow flavors to meld.