Preheat oven to 375 F. Mix butter, sour cream and egg together. Stir in both cans of corn. Blend in dry muffin mix. Spoon into well-greased or Pam sprayed large casserole dish. Mixture puffs up quite a bit while baking so use a larger dish than you think it needs. Bake 1 hour until puffed up and crisp on top.