Preheat your oven to 350°F and lightly butter a small baking dish (about 2-cup capacity works perfectly for two servings). This ensures the oven reaches the proper temperature by the time your casserole is ready to bake, and buttering the dish prevents sticking while adding subtle flavor.

In a medium bowl, whisk together the room-temperature egg yolk, melted butter, sour cream, and kosher salt until smooth and well combined. The room temperature egg yolk is important here—it incorporates more smoothly into the wet ingredients without creating lumps. I prefer full-fat sour cream because it creates a noticeably creamier texture in the finished casserole, which makes a real difference in this simple dish.

Add the cream style corn to the creamy base from Step 2 and stir to combine. Then gently fold in the corn muffin mix until just combined—don't overmix, as this keeps the texture light rather than dense. The batter should be thick and chunky, not smooth.

Pour the batter from Step 3 into your prepared baking dish, spreading it evenly. Sprinkle the shredded sharp Cheddar cheese over the top in an even layer. I use sharp Cheddar instead of mild because the tangier flavor stands up better and doesn't get lost when baked—you actually taste the cheese rather than just a mild dairy presence.

Bake for 35-40 minutes until the top is golden brown and a toothpick inserted into the center comes out clean or with just a few moist crumbs—this indicates the egg has set and the casserole is fully cooked. The baking time may vary slightly depending on your oven, so start checking around 35 minutes.

Remove the casserole from the oven and let it sit for 5 minutes before serving. This resting period allows the structure to set slightly and makes it easier to portion. If desired, top with fresh chopped parsley for a pop of color and fresh flavor just before serving.