Preheat the oven to 350 degrees F.
Gather all ingredients while the oven heats, and ensure the whole kernel corn has been fully drained.
Crack the eggs into a large mixing bowl and lightly beat them with a fork.
Pour in the melted unsalted butter and add the sour cream, then mix gently to begin combining the wet ingredients.
Add the drained whole kernel corn and the creamed corn to the bowl.
Whisk the mixture until the eggs, butter, sour cream, and corn are evenly incorporated.
Add the Jiffy corn muffin mix to the bowl.
Stir until the batter is fully blended and smooth, making sure no dry pockets or large lumps remain.
Grease an 8×8-inch casserole dish with butter to help prevent sticking.
Transfer the corn mixture into the prepared baking dish and spread it into an even layer.
Bake uncovered in the preheated oven for 45 minutes.
The casserole is finished when the surface is golden, the edges show slight cracking, and the center feels set rather than loose or jiggly.
Remove the casserole from the oven and allow it to cool briefly.
Serve warm.