Try the making the dip with sweet onions, it's super delicious. Bake until the crust is well browned. It'll help caramelize everything. You can mix the dip ingredients several days ahead of time, and then bake it off when needed. We've even kept it unbaked in the fridge for a couple weeks and it was still great.
In a bowl, mix together the cream cheese, mayonnaise, parmesan, onion, black pepper and garlic powder until everything is thoroughly combined.