Preheat your oven to 350°F and prepare a 9x13-inch baking dish with butter or cooking spray. This prevents sticking and ensures even browning on all edges of the dish.

Melt 4 tablespoons butter in a large skillet over medium heat, then add corn kernels and sauté for 3-4 minutes until fragrant. Stir frequently to prevent burning on the bottom.

In a medium bowl, whisk together eggs, heavy cream, whole milk, salt, black pepper, garlic powder, and cayenne pepper until completely smooth. This custard base creates the creamy texture that makes this corn casserole absolutely unforgettable.

Remove the skillet from heat and stir in shredded sharp cheddar and mozzarella cheese until melted, then pour in the egg mixture. Fold gently for 30 seconds until everything is combined without overmixing, which can make the texture rubbery.

Pour the entire mixture into your prepared baking dish and spread evenly. Top with combined panko breadcrumbs, melted butter, chopped parsley, and green onions in a thin, even layer.

Bake for 35 minutes until the top turns golden brown and a knife inserted in the center comes out clean. The casserole should be set but still jiggle slightly—this residual heat continues cooking it gently.

Remove from the oven and let this buttery cheesy corn casserole recipe rest for 5 minutes before serving. This cooling period allows the custard to set completely so portions maintain their shape when plated.