Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish with butter or non-stick cooking spray. I've found that taking the time to grease the dish thoroughly ensures that every golden, cheesy piece comes out easily, without leaving half of it stuck to the bottom.

In a large mixing bowl, combine the drained whole kernel corn and creamed corn. Here's where I learned my lesson: make sure to drain the whole kernel corn well. Any excess liquid can throw off the balance of the dish, leading to a less-than-perfect casserole texture.

Add the sour cream and melted butter to the corn mixture. The sour cream is the secret to that irresistible creaminess, while the butter adds a rich, velvety texture that makes the casserole truly indulgent. Stir these in until well combined.

Fold in the shredded cheddar cheese. I remember the first time I made this, I mixed the cheese in too vigorously and ended up with a less-than-ideal distribution. A gentle fold is all it takes to ensure that every bite is filled with cheesy goodness.

Sprinkle the Jiffy corn muffin mix over the corn and cheese mixture. Then, add the beaten eggs, salt, and black pepper. If you're feeling adventurous, this is the time to add the diced jalapeño for that extra kick. Mix everything together until just combined. Overmixing can lead to a dense casserole, so mix until you no longer see dry spots of muffin mix.

Pour the batter into the prepared baking dish, smoothing the top with a spatula. I've found that starting from the center and working your way out to the edges ensures an even layer, which helps the casserole cook uniformly.

Bake in the preheated oven for 45-50 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean. The key here is patience; don't be tempted to pull it out too early. That golden crust is worth the wait and provides a delightful contrast to the creamy interior.

Allow the casserole to rest for at least 5 minutes before serving. This resting period lets the casserole set, making it easier to slice and serve without it falling apart. It's a small step that makes a big difference in presentation and texture.