Preheat your oven to 350°F (175°C) and lightly grease a 2 1/2-quart casserole dish.
In a large pot, add lightly salted water and bring it to a boil.
Once boiling, add whole, unpeeled potatoes and cook until they are tender, which should take about 25 to 30 minutes.
Once cooked, transfer the potatoes to a cutting board and discard the water.
After they have cooled enough to handle, peel the potatoes and grate them into a medium bowl.
In a large skillet, melt 1/4 cup of butter over medium heat.
Stir in the soup and cook until it starts to bubble.
Remove the skillet from the heat and mix in sour cream, Cheddar cheese, and green onions.
Finally, fold in the grated potatoes until well combined.
Pour the potato mixture into the prepared casserole dish.
In a resealable plastic bag, combine cornflake crumbs with 2 tablespoons of melted butter.
Shake the bag until the crumbs are evenly coated.
Sprinkle this mixture over the top of the casserole.
Bake in the preheated oven for 45 minutes until golden and bubbly.