Preheat oven to 350 degrees. Melt 1/4 cup butter in an 8x8 casserole dish in the oven while it heats. Meanwhile, combine hash browns, green onion, sour cream, cheese and soup in a large bowl. Transfer mixture to the casserole dish after the butter has melted. Bake, uncovered, for 30 minutes. Melt remaining 1/4 cup butter in the microwave, then mix with crushed cornflakes. Sprinkle on top of the potatoes then bake for 15 more minutes.