First, take a 4-quart casserole dish and butter the bottom and sides. Then mix together well the flour, salt and black pepper, and preheat your oven to 350F degrees. Next, take one-third of the Potatoes and make a layer on the bottom of the casserole dish. Then sprinkle the slices gently with one-third of the flour mixture. Then sprinkle on one-third of the onions, green onions and parsley. [I'd mix these together well and then separate into thirds.] Repeat this process until you "layer on" all the Potatoes, flour, onions, green onions and parsley. Now, scald the milk and melt the butter into it. And when thoroughly blended, gently pour the mixture uniformly over the layer Potatoes. At this point, cover the casserole with tight-fitting aluminum foil and bake for 30 minutes. Then uncover the dish and bake for another hour (or until the Potatoes are browned and tender). Serve 'em piping hot! And you'd better have enough for seconds!