Step 1: Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish or a 2-quart casserole dish with butter or non-stick spray.
Step 2: In a large bowl, whisk together the melted butter, sour cream, and beaten eggs until the mixture is smooth and well combined.
Step 3: Stir in the drained whole kernel corn and the undrained cream-style corn into the wet mixture.
Step 4: Add the Jiffy Corn Muffin Mix to the bowl and stir gently until just incorporated; do not overmix the batter.
Step 5: Pour the batter into the prepared baking dish and spread it evenly with a spatula.
Step 6: Bake for 45 to 50 minutes, or until the top is golden brown and the center is set but still slightly soft.
Step 7: Remove from the oven and let the casserole rest for 10 minutes before serving to allow the texture to firm up.