Preheat and Prepare Your Dish: Preheat your oven to 350°F (175°C). Generously grease an 8×8 inch or 9×9 inch square baking dish (a 2-quart casserole dish also works perfectly). Greasing the dish well is essential for easy removal and prevents the casserole from sticking.

Combine the Wet Ingredients: In a large mixing bowl, combine the can of drained whole kernel corn, the undrained can of creamed corn, the sour cream, the melted butter, and the two lightly beaten eggs. Stir everything together until it is well combined.

Add the Dry Mix: Pour the entire box of Jiffy Corn Muffin Mix into the wet ingredients. Stir gently with a spoon or spatula until just combined. It’s important not to overmix; a few small lumps are perfectly fine. Overmixing can develop the gluten and result in a tougher, denser casserole.

Incorporate Optional Cheese: If you are using shredded cheese, fold it into the batter now, reserving a small handful to sprinkle on top if you wish.

Pour and Spread: Pour the batter into your prepared baking dish and use the spatula to spread it into an even layer. If you reserved any cheese, sprinkle it evenly over the top of the batter now.

Bake to Golden Perfection: Place the baking dish in the center of the preheated oven. Bake for 45 to 55 minutes. The casserole is done when the edges are golden brown and pulling away slightly from the sides of the dish, and the center is mostly set. A knife or toothpick inserted into the center should come out with moist crumbs attached, but not wet batter.

Rest Before Serving: This is a crucial step! Remove the casserole from the oven and let it cool on a wire rack for at least 10-15 minutes before serving. This allows the casserole to set up properly, making it easier to slice or scoop. Serving it straight from the oven will cause it to be runny and fall apart.