Melt the butter in a skillet over medium-high heat; add onion and cook until onion is soft and translucent. Add corn and serrano pepper and cook until corn starts to turn golden brown, about 5 minutes. Set aside.
In a medium bowl, add cheese, parsley, sour cream and stir. Season with salt and pepper. Add corn mixture and chopped tomatoes and stir until it's well mixed. Pour the mixture into a baking dish and top with additional cheese if preferred.
Bake for about 15 minutes or until cheese is bubbling and the top is golden.
Please keep in mind that nutritional information is a rough estimate and can vary greatly based on products used.