Cook potatoes in boiling salted water until tender. Drain and return pan to low heat, shaking to dry potatoes. In large bowl of electric mixer, cream together cheese and sour cream. Add hot potatoes one at a time to cream mixture and continue beating at high speed until light and fluffy. On low speed, add minced onions, celery, green pepper, parsley, melted butter, garlic powder, salt and pepper. Spoon into a 2 1/2 to 3-quart baking dish. Sprinkle with paprika and dot with 2 tablespoons butter or margarine. Bake at 375° for 25 minutes or until top is golden.