Place large potato pieces in a large pot and cover with water. Generously salt the water (about 2 tsp). If using store-bought hash browns, skip to #5.
Bring to a boil and cook until potatoes are fork-tender, about 20 minutes.
Drain and let cool to a temperature that you can handle touching.
Using the large grate side of your cheese grater, grate the potato pieces. Put grated potatoes in a large bowl, and set aside.
In a deep frying pan or two-quart saucepan, saute the chopped onion in the 3 tbsp of butter for 3-4 minutes until they are clear and tender.
Add sour cream and both creamed soups. Stir well until heated throughout.
Pour mixture over grated potatoes and stir until well combined.
Add the shredded cheese and stir until combined.
Pour mixture into a lightly greased 9x13 pan. The mixture should come up to about ⅔ or ¾ of the height of the pan. (If you have too much mixture, put some in a second pan and freeze it for another time.)
For the cornflake topping, in a medium bowl, combine cornflakes and 3 tbsp of butter. Mix until combined. Sprinkle the cornflake mixture evenly on top of the potato mixture. (This step is optional.)
Bake in a 350-degree oven for 45-60 minutes or until bubbling on the sides and hot in the center.
If you don't want the cornflakes on top, sprinkle an additional cup of shredded cheese on top during the last 10 minutes of cooking.
Recipe by Real Life Dinner at https://reallifedinner.com/yummy-funeral-potatoes/