Cheesy Au Gratin Potatoes

Potatoes:
3 Tbsp butter
1 Lrg onion, chopped
1/4 C all purpose flour
1 1/2 C chicken broth
1 C milk
1 1/2 tsp salt
1/2 tsp pepper
1/2 tsp dried thyme
2 C shredded cheddar cheese
26 oz-bag frozen shredded hash browns (I used real potatoes, just cook the dish longer)
1/2 C sour cream

Topping:
3 C cornflakes, lightly crushed
2 Tbsp butter, melted

Melt the butter in a large pot over medium heat. Add the onion until it is soft. Stir in the flour, cook, stirring constantly, for about a minute. Combine the broth and milk in a liquid measuring cup and slowly whisk into the onion mixture. Add the salt, pepper, and thyme. Stir to combine. Bring the mixture to a boil and then reduce the heat to medium-low and simmer, stirring frequently, until the mixture is slightly thickened, about 5 minutes.

Take the pot off the heat and stir in the cheese until smooth. Mix in the potatoes and then fold in the sour cream.

In medium bowl, toss the cornflakes with the butter until evenly combined. Pour the potato mixture into a 9x1 baking dish and top with buttered cornflakes. Bake at 350 degrees for 45 minutes. Longer if you are using raw potatoes, just keep checking them until the potatoes are at your desired texture. Let sit 10 minutes before serving.