Preheat the oven to 375°F (190°C). Set out an 8 x 8-inch (20 x 20 cm) baking dish with approximately 2-quart (1.9 L) capacity. The butter in the filling provides richness, so additional greasing is generally unnecessary for a standard nonstick or glazed ceramic dish.

Place the 4 cups (about 660 g) of thawed sweet corn in a strainer and allow any excess moisture to drain away. Gently blot the kernels if they still appear wet. The corn should be moist but not dripping, since extra liquid can make the baked filling watery.

Place the 8 ounces (225 g) full-fat block cream cheese, softened and cubed, in a medium microwave-safe bowl. Warm briefly in the microwave only if it is still too firm to stir. Add the 1/2 cup (120 g) full-fat sour cream and 2 tablespoons (28 g) unsalted butter, melted and slightly cooled. Mix until thick, smooth, and mostly free of cream cheese lumps. The mixture should spread easily rather than pour like a thin sauce.

Stir in the 1/2 teaspoon (3 g) fine salt, 1/4 teaspoon (0.5 g) freshly ground black pepper, 1/2 teaspoon (1.5 g) garlic powder, and 1/2 teaspoon (1 g) onion powder. Mix until the seasonings are evenly dispersed throughout the cream cheese base.

Transfer the seasoned cream cheese mixture to a large bowl if necessary. Fold in the drained sweet corn and 1 cup (113 g) of shredded sharp cheddar cheese. Stir until the kernels are evenly coated. The mixture should be thick and scoopable, with visible corn kernels and no pool of liquid at the bottom.

Spoon the corn mixture into the prepared baking dish. Spread it into an even layer with a spatula, smoothing the top without pressing it down tightly. Sprinkle the remaining 1/2 cup (57 g) shredded sharp cheddar cheese evenly across the surface.

Place the uncovered dish on the center oven rack and bake at 375°F (190°C) for 35 minutes. The cheese should be melted, the edges should be gently bubbling, and the center should look hot and creamy rather than watery. If the top browns too quickly, cover loosely with aluminum foil for the remainder of baking.

Remove the casserole from the oven and let it rest for 5 minutes. The creamy filling will settle slightly while remaining soft and spoonable. Serve warm, scooping through the melted cheddar topping to include plenty of corn and creamy filling in each portion.