In a medium saucepan over medium heat, melt ¼ cup salted butter. Once melted, add in the finely diced 1 medium white onionhite onion and cook, stirring occasionally, until softened and lightly browned, about 5 minutes.

Sprinkle in ¼ cup all-purpose flour, stirring continuously for about 2–3 minutes, until the mixture is smooth and turns a deep golden color.

Gradually pour in 1 cup chicken brothStir in 1 cup heavy cream and 1 cup sour creamuntil the sauce is smooth and fully combined. Lower the heat to a simmer and cook for an additional 2–3 minutes, stirring occasionally.

Stir in 1 tablespoon chopped fresh parsley, 1 tablespoon garlic powder, 1 teaspoon hot sauce, 1 teaspoon black pepper, and 1 teaspoon salt. Remove from heat and set aside.

Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch or 3-quart baking dish.

Using a grater or food processor, grate 6 large russet potatoes. Rinse the grated potatoes in a colander under cold water and squeeze out any excess moisture. Transfer the potatoes to a large mixing bowl.

Pour the prepared sauce over the grated potatoes. Add 1 cup of the shredded cheddar cheese and gently stir until well combined.

Spread the potato mixture evenly in the prepared baking dish. Sprinkle the remaining 1 cup cheddar cheese and 1 cup crushed corn flakes over the top. Drizzle 2 tablespoons of melted butter evenly over the casserole.

Bake in the preheated oven for about 1 hour, or until the potatoes are tender and the top is golden brown and crispy. Serve hot.