Melt the butter in a large skillet over medium heat until foamy.

Add chopped onions, sprinkle with salt and pepper, and reduce to low heat. Cook slowly for 30 to 60 minutes until caramelized.

Remove from heat and let onions cool slightly.

In a mixing bowl, combine sour cream, mayonnaise, and garlic powder until smooth.

Fold cooled onions into the dip mixture gently until evenly distributed.

Cover and refrigerate for at least 30 minutes before serving.