Make ahead Mashed Potatoes

8-10 medium potatoes, peeled ind boiled til tender
1 c. sour cream
1-8oz. cream cheese softened
4 T. butter
salt and pepper to taste
1/2 c. parmeasan cheese
Beat the sour cream and creamed cheese together.  Add hot drained potatoes. beat until smooth.  Add butter, salt and pepper.  Dot with butter and sprinkle with cheese.  Refrigerate 2-3 days.  When ready to serve, bake at 350 for 25 minutes until golden.