If using fresh russet potatoes, peel and cut them in half. Boil in a large pot of salted water with a splash of apple cider vinegar for about 10 minutes, or until tender. Drain, then let cool for a few minutes before grating. If using frozen hash browns, let them thaw in the refrigerator overnight until they’re ready to go.

Preheat your oven to 350ºF (175ºC). While the oven is heating, butter a 9x13-inch baking pan generously.

In a skillet, melt 2 tablespoons of unsalted butter over medium heat. Add 1 finely diced yellow onion and sauté for about 5-7 minutes until soft and translucent. Then, add 2 minced garlic cloves, cooking for an additional minute until fragrant.

Sprinkle 1/4 cup of all-purpose flour into the onion mixture, stirring to create a roux. Gradually whisk in 1 cup of low-sodium chicken broth and 1 cup of whole milk, continuing to stir until it thickens, about 5-7 minutes. Remove from heat, stirring in 2 cups of extra-sharp cheddar cheese and 1 cup of sour cream.

In a large bowl, gently fold the grated potatoes into your rich cheese sauce until they are well coated. Transfer this mixture to your prepared baking pan.

In a small bowl, crush 2 cups of cornflakes, then mix in 2 tablespoons of melted butter until evenly coated. Spread it generously over the casserole.

Place the baking dish in your preheated oven, and bake for 45-60 minutes, or until the top is golden-brown and bubbly. Let it cool for 10-15 minutes before serving.