Cut the ham into thin irregular slices about 1 by 1 by 1/8-inch and saute briefly in the butter with the shallots or scallions, just to warm through thoroughly. Remove from the heat. In a small bowl, beat the egg yolks with the cream; stir this mixture into the ham along with drops of Worcestershire and pepper sauce and freshly ground pepper to taste. Warm over low heat, folding the ham into the sauce, until it thickens but does not boil. Set aside to cool and thicken even more. It should be cold when it goes into the Pithiviers. Roll the dough out into a rectangle about 18 by 9 inches and cut into thirds crosswise; refrigerate 2 pieces, wrapping and storing one of them for another use. Roll remaining pieces, which will be the bottom of the tart, into a square 12 inches to a side; using a pie plate or cake pan to guide you, cut a 9 1/2-inch disk out of the center of the dough. Remove surrounding dough and set on a bake sheet for reconstituting later. Lightly fold disk in half and set upside down on dampened baking surface. Roll out second piece of dough to a thickness slightly more than 1/4-inch and cut into a disk the same size as the first. Refrigerate it along with the surrounding dough pieces from both disks. With the balls of you fingers, push and pat the bottom disk of the dough out onto its baking surface to make an even circle slightly larger than your cutting guide. With a roller-pricker or two forks, prick the dough all over at 1/2-inch intervals, going down through dough to pastry sheet to keep this bottom layer from rising too much. Form the ham into a round cake about 4 1/2 inches across and place in the center of the dough. It is important to leave a 2-inch border of clear dough all around the ham to prevent leakage of the filling during baking. Preheat the oven to 425 degrees.
Paint the border of the dough with cold water, and immediately center the top layer in place, stretching gently as necessary. With a sharp-pointed knife make a little hole 1/8- inch wide in the center of the dough, going down into the filling, to allow for escaping steam during baking, Then, with the ball of your first three fingers, firmly press the two pieces of dough in place all around. Bake the Pithiviers for about 20 minutes, until it has puffed and is beginning to brown nicely. Turn down the oven to 400 degrees F and continue to bake for 20 to 30 minutes. If the Pithivier begins to brown too quickly, cover the pie with foil loosely and continue to bake. Remove from the oven and allow to rest for 5 minutes before slicing. Slice the pie into wedges.
Yield: 8 to 10 servings
Recipe from "Cooking with Company", Julia Child, Knopf Publishers, 1978