01 - Preheat your oven to 350°F (175°C). Grease a 9x9-inch baking dish or similar casserole dish with butter or cooking spray.
02 - In a large bowl, combine the drained whole kernel corn, creamed corn, sour cream, melted butter, and Jiffy corn muffin mix. Mix until just blended—do not overmix.
03 - If using shredded cheddar cheese, fold it gently into the mixture until evenly distributed.
04 - Pour the mixture into the prepared baking dish and spread evenly using a silicone spatula.
05 - Bake for 45–50 minutes, or until the top is golden brown and the center is set. A toothpick inserted into the center should come out clean.
06 - Remove from oven and let the casserole rest for 5 minutes before serving. This allows it to set and makes serving easier.