To make the custard, in a small bowl whisk together the cornstarch, sugar, ½ cup of the half-and-half, and the egg yolks until smooth. Heat the remaining 1 cup half-and-half in a medium saucepan over medium heat until it is scalded--you will see steam rising from the surface and small bubbles around the edges. Very gradually, add the hot half-and-half to the egg yolk mixture, whisking constantly. Scrape the mixture into the saucepan and cook over medium heat, stirring constantly with a heatproof rubber spatula, until the custard thickens, about 5 minutes. Because it is so thick, the custard will never actually boil, and as it heats, it will gradually become lumpy, especially on the bottom. Just keep stirring, going all around the sides and bottom of the pan with the spatula. As it thickens further, the custard will look like scrambled eggs. At this point, switch to the whisk and stir, don’t beat, until very smooth. Cook, whisking, for 1 to 2 minutes more. Remove the pan from the heat, scrape the custard into a medium bowl and stir in the vanilla. Press a piece of plastic wrap directly onto the surface of the custard to prevent a skin from forming, and cool for 30 minutes at room temperature, then refrigerate until very cold. (The custard can be made a day ahead.)

To make the cake, adjust an oven rack to the lower third position and preheat the oven to 350°F. Butter a 9-inch spring form pan or coat it with cooking spray. Line the bottom of the pan with a round of cooking parchment or waxed paper and butter the paper. Dust the inside of the pan with fine dry bread crumbs and tap our the excess crumbs.

Sift the flour, potato starch, and baking powder together twice.

In a large bowl, whip the egg whites and salt with an electric mixer on medium speed until the whites are shiny and form stiff peaks when the beaters are raised. Do not overbeat--the whites should be smooth, not lumpy. Beating on medium speed, sprinkle in about one-quarter of the sugar, then add 1 egg yolk and beat for about 10 seconds. Repeat the process 3 more times, then continue beating a few minutes more, until the mixture is thick and pale and forms a slowly dissolving ribbon when the beaters are raised.

Using a large rubber spatula, gently fold in the flour mixture in 4 additions, only until no dry ingredients show. Scrape the batter into the prepared pan, and gently smooth the top.

Bake for about 30 minutes, until the cake is golden brown and springs back when gently pressed and a toothpick inserted into the center comes out clean. Cool the cake in its pan on a wire rack for 10 minutes. Run the blade of a small sharp knife around the sides of the cake to release from the pan, if necessary, and carefully remove the sides of the pan. Cover the cake with a wire rack and invert. Remove the bottom of the pan and the paper liner. Cover the cake with another wire rack and invert again to cool completely right side up.

To assemble the torte, use a long sharp serrated knife to split the cake into 3 equal layers; set aside.

Whip the cream in a large bowl until it is thick and holds a firm shape. Transfer one-third of the cream to a small bowl, cover, and refrigerate. Remove the chilled custard from the refrigerator; it will be very thick. Whisk it vigorously until it is smooth and creamy. Fold half the remaining whipped cream into the chilled custard, then fold the custard into the remaining cream.

Arrange strips of waxed paper in a square pattern around the edges of a serving platter. Set the bottom cake layer, cut side up, onto the platter, with the edges of the waxed paper strips just under the edge of the cake. Spread the raspberry jam onto the cake, then spread half the custard cream mixture evenly over the jam. Invert the top cake layer onto the custard cream so that its cut side is facing up. Spread the remaining custard cream over the layer and place the remaining cake layer on top. Spread about one-quarter of the reserved refrigerated whipped cream in a very thin layer around the sides of the cake. Scrape the remaining cream onto the top of the cake and spread evenly with a narrow metal spatula. Carefully remove the waxed paper strips by pulling them toward you gently by a short end. Refrigerate the cake.

To make the marzipan coating, break the marzipan into small pieces into a medium bowl. Add 3 or 4 drops of green food coloring and knead it into the marzipan with your hands to tint the marzipan a shade of pale green. The marzipan is stiff, so be patient. Add a drop or two more of food coloring if necessary, but don’t tint the marzipan a bright green. Dust your work surface with confectioners’ sugar. Shape the marzipan into a 6-inch disk, place it on the work surface, and turn to coat both sides lightly with sugar. Roll the marzipan to a circle about 16 inches in diameter and less than 1/8 inch thick. Turn the marzipan over during the rolling and dust it with the confectioners’ sugar as necessary to prevent slicking. (If you have 18-inch-wide plastic wrap, you can roll the marzipan between two sheets of it instead.)

Remove the cake from the refrigerator. Fold the circle of marzipan in half and gently set it on the top of the cake, with the fold on the center. Carefully unfold the marzipan so that it drapes over the cake, then fold the edges of the marzipan over and press it gently so it adheres to the sides of the cake, covering the cake completely. Try to avoid wrinkling the marzipan. Use a sharp knife to trim away the excess marzipan so that the edges are flush with the platter. Refrigerate until ready to serve.

To serve, dust the top of the cake with confectioners’ sugar. Use a sharp knife to score portions in the marzipan and then cut the cake.