1.Preheat Oven To 350 Degrees F (175 Degrees C). 2.In A Mixing Bowl, Combine Butter, Mayonnaise, Sour Cream And Lemon Juice. 3.Place Cod Fillets In A 8X8 Inch Baking Dish. Pour Mayonnaise Mixture Over Fish. 4.Bake In A Preheated Oven For 30 Minutes Or Until Fish Flakes Easily With A Fork.