Saute chopped onion in a small skillet coated with vegetable cooking spray until tender.
Prepare corn muffin batter according to package directions; pour into a lightly greased 8-inch square pan, and top with onion. Stir together sour cream and cheese; spread over onion.
Bake at 400° for 25 minutes or until golden brown. Let stand 10 minutes before cutting.
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