Preheat oven to 350 degrees. Spray a 2 quart casserole with non-stick spray.
In a large bowl, mix together sour cream, mayonnaise, garlic powder, extra sharp white cheddar cheese and 1/4 cup of the green onions. Stir.
Blend corn into sour cream mixture and blend until it is incorporated.
Separate the mixture equally. Place half of the mixture into a blender or food processor and puree. Return puree to the corn mixture, and stir well. Pour mixture into prepared casserole dish.
Back 40-50 minutes or until hot & bubbly. In the last 5 minutes of baking, sprinkle the cheddar cheese on top. Finish cooking and remove from oven.
Garnish with green onions. Serve with pita chips, corn dips or bread.