Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish.
Combine whole kernel corn, creamed corn, sour cream, melted butter, and beaten eggs in a large bowl. Stir until uniform.
Add corn muffin mix. Fold in gently until no dry streaks remain. Do not overmix.
Pour into the prepared baking dish and spread evenly.
Bake uncovered for 40 minutes. Add cheddar if using, then bake another 10 minutes until the top is deep golden and a toothpick inserted 2 inches from the center comes out clean (165°F / 74°C internal temperature).
Rest on a wire rack for 10 minutes before slicing.