Preheat oven to 350 degrees.
Lightly spray a 2 quart baking dish.
Combine the mayonnaise, cream cheese,Parmesan cheese and garlic in a large bowl, beat with an electric mixer until well blended and smooth.
Add the chopped onions and mix until well combined. Season with salt and pepper.
Bake for 45 minutes or until lightly browned on top. Serve with butter crackers.