Bake the potatoes, skins on, in the center of a preheated 450-degree oven for 40 minutes. This will be a bit less than the time needed for edible baked potatoes. Cool the potatoes, then refrigerate.
When you're ready to cook, remove the potatoes from the refrigerator and cut in half, but leave the peels on.
In a skillet over the highest heat, melt 2 Tbs. butter until it sizzles. Using the big holes on a hand grater, grate the potatoes right into the pan, sprinkling some green onions as you go, until the pan is nearly full. Cook without turning until the bottom appears to be on the verge of burning. Turn (either the whole thing or as much as you can at a time) and cook the same way on the other side.
Dump the pan of hash browns into a serving dish, and keep it warm in the oven while you repeat the process for the rest of the potatoes. Or you can stop right there if that's enough for the meal involved. The rest of the potatoes can be made into hash browns on another occasion.