01 -
Preheat the oven to 350°F. Lightly grease or butter a 9×13 baking dish and set aside.
02 -
Combine shredded cheddar and Monterey Jack cheeses in a small bowl and toss to combine. Set aside.
03 -
Place defrosted potatoes in a large bowl. Toss with 4 tablespoons of melted butter, salt, and pepper. Stir in sour cream and 2 cups of the cheese mixture. Set aside.
04 -
Melt 4 tablespoons of butter in a skillet over medium heat. Add onions and sauté until translucent, about 4-5 minutes. Add minced garlic and cook for an additional minute, stirring frequently.
05 -
Sprinkle the flour into the skillet and cook, stirring, for 1 minute. Slowly whisk in chicken broth until smooth. Gradually whisk in milk until fully combined. Bring to a simmer, season with salt and pepper, and cook for 3-4 minutes until thickened. Remove from heat.
06 -
Pour the cream sauce over the potato mixture and gently fold to combine. Transfer to the prepared baking dish. Top with the remaining cheese.
07 -
In a bowl, combine 4 tablespoons of melted butter with crushed cornflakes, tossing to coat evenly. Spread the topping over the cheese layer in an even layer.
08 -
Cover the dish with foil and bake for 20 minutes. Remove foil and bake for another 15-20 minutes or until the edges are bubbling and the cornflakes are golden brown.
09 -
Allow the casserole to rest for 10 minutes before serving.