Cook the potatoes in lightly salted water to cover until the potatoes are very soft. Drain and allow to cool slightly, then peel, mash by hand and let cool further. Add 1-teaspoon salt, the flour and eggs and mix well to form a smooth paste. Spread this mixture onto a sheet of clean cheesecloth, to form a rectangle measuring 15 by 12 inches.
In a large skillet, heat the oil over high heat. Add the onion and cook until soft. Add the escarole, pepper and 1/2-teaspoon salt and cook, stirring, for 5 minutes, or until most of the moisture has evaporated. Spread this mixture over the potato rectangle, leaving a 1/2-inch margin on the perimeter.
Roll the short way, using the cheesecloth as a rolling tool, so that the potato rectangle is shaped like a jelly roll. Wrap the roll in the cheesecloth and fasten the ends with string.
In a fish poacher or pot large enough to hold the roll, bring 2 quarts of water to a boil and add 1-tablespoon salt. Gently lower the roll into the water and return to the boil. Lower to a simmer, and cover. Cook 45 minutes to 1 hour. Transfer the roll to a warm dish and let rest 10 minutes. Remove the cheesecloth, cut the roll into 12 slices and drizzle the melted butter and cheese over.
Recipe copyright 2000, Mario Batali. All Rights Reserved.