Begin by preheating your oven to 375 degrees Fahrenheit. Take a medium sized baking dish and lightly grease it with butter or a small amount of oil to ensure nothing sticks. If you are using frozen corn, make sure it has been thawed and patted dry with a paper towel to prevent the sauce from becoming too watery during the baking process.
In a large saucepan or skillet over medium heat, melt the 1/4 cup of butter. Once it is bubbling, whisk in the all purpose flour. Continue to whisk for about one minute to cook out the raw flour taste. You want the mixture to be smooth and slightly pale, taking care not to let it turn brown.
Slowly pour in the heavy cream and whole milk while whisking constantly. This gradual process helps to prevent lumps from forming. Continue to cook the mixture over medium heat until it starts to thicken into a silky sauce. Stir in the salt, black pepper, and garlic powder to evenly distribute the seasonings.
Add the corn kernels into the saucepan and stir until they are completely coated in the cream sauce. Remove the pan from the heat and fold in one cup of the shredded cheddar cheese. Stir until the cheese is mostly melted and the mixture is thick and creamy.
Transfer the corn mixture into your prepared baking dish. In a small bowl, combine the panko breadcrumbs, the remaining half cup of cheese, and the melted butter. Sprinkle this crumbly mixture evenly over the top of the corn. Place the dish in the oven and bake for 20 to 25 minutes, or until the sauce is bubbling and the topping has turned a perfect golden brown. Let it sit for a few minutes before serving to allow the sauce to set.
