Heat a small skillet over medium heat and add the butter. When the butter melts, add the onion. Saute until mostly tender and beginning to brown, about 5-7 minutes. Remove from heat and let cool to room temperature.
In a medium bowl, mix together the cans of corn, muffin mix, sour cream, pepper, and onion and butter until well combined. Pour into a medium baking dish, spreading in an even layer.
Transfer to the oven and bake for 45-60 minutes or until the souffle is set in the center and golden brown on the edges.