For the pasta frolla, combine the dry ingredients and mix well. Rub in the butter until it is absorbed, making sure the mixture remains cool and powdery and does not become pasty. Beat the egg and stir in with a fork. Continue stirring until the dough holds together, then knead it briefly, just until smooth. Shape into a disk, wrap in plastic, and refrigerate at least 1 hour, or until firm.
For the filling, cut the pumpkin into 2-inch dice, scrape away the filaments, and peel off the skin. Steam the pumpkin over simmering water for about 40 minutes, until it is tender. Puree the pumpkin in a blender or a food processor fitted with the metal blade and cool. If the pumpkin puree is excessively watery, cook it, stirring constantly, over medium heat, preferably in a nonstick pan, to dry it out before cooling.
Measure 2 cups of the pumpkin puree (a little more or less won’t matter) into a large mixing bowl. Whisk in the sugar, cinnamon, and eggs, one at a time. Combine the ground almonds and cornmeal and stir into the pumpkin mixture. Place the candied orange peel in a strainer, rinse it under running water, and chop it finely with a sharp knife. Oil the blade of the knife to prevent it from sticking to the peel. Stir the chopped peel into the filling, then fold in the melted butter.
To assemble the crostata, roll the dough out on a floured surface into a large disk, about 14 inches in diameter. Fold the disk of dough in half and fit it into a buttered 9-inch × 2-inch-deep layer cake pan. Press the dough well against the bottom and sides of the pan and trim the edges of the dough so they are even with the top of the pan. Pour in the filling and spread it evenly. The filling will be about ½ inch lower than the top of the pan. Fold the excess dough at the rim inward, over the filling, so that it makes a border about ½ inch wide at the edge.
Bake the crostata in the lower third of a preheated 350-degree oven for about 45 minutes, until the filling is set and the dough is a light golden color. Cool the crostata in the pan on a rack. When the crostata is completely cooled, place a flat plate or pan on top and invert. Lift off the baking pan and replace it with a platter. Invert again and remove the top plate or pan. Keep the crostata loosely covered at room temperature.