Preheat the oven to 350 degrees.
Add 2 tablespoons of butter to a medium sized skillet and add the diced garlic and minced onion.
Cook the garlic and onion over medium heat until the onion is soft, around 5-7 minutes.
In a large mixing bowl, add the onion and garlic mixture, thawed hash browns, cream of mushroom soup, sour cream, parmesan, salt, and 1 cup of the fresh grated cheddar cheese.
Mix the filling well, then spread it out into a greased 9 X 13 baking dish.
Top the hash brown potatoes with the remaining 1 cup of cheddar cheese.
Measure 3 cups of corn flakes and place in a ziploc bag. Crush them up with your hands.
Melt the remaining 3 tablespoons of butter and mix it in a bowl with the crushed corn flakes.
Spread the cornflake topping over the top of the casserole in an even layer.
Bake the cheesy potatoes with corn flakes at 350 degrees for 50-60 minutes, until bubbly and browned on top