Preheat the oven to 350°F. Generously spray a 9x9-inch baking dish with baker's spray (I used Baker's Joy, but you can use a generic version). Set it aside.
Add the sour cream, melted butter, and eggs to a medium-sized mixing bowl. Whisk to combine.
Stir in the corn muffin mix, undrained cream corn, and the drained whole kernel corn. Stir just until incorporated.
Evenly spread the mixture into the prepared baking dish. Bake For 50 to 55 minutes until golden brown. Serve while hot.
You can prepare this creamy corn casserole up to 48 hours in advance and store it in the fridge covered in plastic wrap. When you’re ready to bake, simply remove it and set it on the counter for 30 minutes before popping it in the oven.
Oven temperatures vary and may need to be recalibrated periodically to ensure they are accurate. Make sure to check your casserole at the lower end of the recommended cooking time.