Preheat the oven to 350°F and spray a large casserole dish with cooking spray. Peel the potatoes and slice them into ¼-inch wheels.
Mix the sour cream, chicken soup, cheddar cheese, and spring onions together in a large bowl. Season with salt and pepper to taste. Add the sliced potatoes and stir until all the potatoes are coated.
Pack the potato mixture into the sprayed casserole dish.
In a separate bowl, mix the melted butter with the cornflakes until well-coated. Layer the buttered cereal on top of the potato mixture. Bake in the oven for 1 hour or until the potatoes are cooked through.