preheat to 350F. Tear off two 24-inch pieces of 18-inch-wide heavy-duty aluminum foil. Line a 10-by-15-inch rimmed baking sheet with the foil, crisscrossing the pieces and leaving an overhang on all sides. Fold over each overhang so it stands upright and forms a sturdy wall about 3 inches high. Crimp the corners together, and lightly coat the bottom and sides with the cooking spray.
For the dough: Beat the butter, confectioners’ sugar and salt in a large bowl with an electric mixer on medium-high until smooth, about 1 minute. Add half the flour, and beat to incorporate; add the remaining flour, and beat until the dough just starts to come together in large, soft clumps. Set aside 1/3 of the dough for decorating.
Press half the remaining dough into the bottom of the baking sheet until it is completely covered. Press the remaining dough into and about 1 inch up the sides of the foil wall until the dough is about 1/4 inch thick and there are no gaps where the sides and bottom meet. Bake until the dough is light golden, 20 to 25 minutes. Let cool completely on a rack.
Meanwhile, roll out extra dough to about 1/8 inch thick. Cut out rounds with a piping top OR what would work better: a 1-inch round cookie cutter. Lay all the rounds out on a parchment-lined baking sheet or platter, beat the egg with a little water and brush the tops of each round with the egg wash. Refrigerate until ready to use.
For the filling: Gently whisk together the pumpkin, cream, granulated sugar, eggs, cinnamon, nutmeg, vanilla and salt in a large bowl until blended well. Pour the filling into the cooled pie shell. Press the rounds in a single line all around the edges of the crust. Bake until the filling is only slightly wiggly when shaken, 50 minutes to 1 hour. Let cool completely. Wrap and refrigerate overnight. Cut into squares, and serve with whipped cream.
