Preheat oven to 325°. In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add eggs, 1 at a time, beating well after each addition. Beat in sour cream. Gradually add muffin mix alternately with milk. Fold in corn.
Pour into a greased 3-qt. baking dish or 13x9-in. baking pan. Bake, uncovered, until set and lightly browned, 45-50 minutes.