Cream Cheese Potatoes

9 large potatoes, cooked and mashed
8 oz cream cheese, softened
1 cup plain yogurt or sour cream
2 tbsp butter
2 tsp onion salt
1 tsp salt
pepper to taste

Mash all together well. Turn into a greased casserole dish and dot with butter. Bake uncovered at 350 degrees F for 1/2 hour.