Sauté onions in a skillet over medium heat with butter until golden brown (about 10 minutes).

In a mixing bowl, blend cream cheese, sour cream, garlic powder, salt, and pepper until smooth.

Fold in cheddar and Parmesan cheeses until fully combined.

Mix sautéed onions into the cheese mixture.

Transfer to a baking dish and bake at 350°F (175°C) for 20-25 minutes until bubbly and golden.

Let cool slightly before serving warm with tortilla chips or veggies.