Heat olive oil in a skillet over medium heat. Add sliced onions and cook until caramelized, about 30 minutes, stirring occasionally.

In a mixing bowl, combine sour cream, mayonnaise, garlic powder, salt, and pepper. Stir until well blended.

Once the onions are caramelized, let them cool slightly, then fold them into the sour cream mixture.

Transfer the dip to a serving bowl and refrigerate for at least 30 minutes before serving to allow flavors to meld.