Instructions: CAKE: Arrange two racks in the center of oven, and heat oven to 350 degrees. Line the bottoms of two 8- by 2-inch buttered cake pans with buttered parchment paper. Dust the bottoms and sides of pans with flour, and tap out any excess.

Sift together the flour, baking powder, baking soda, and salt; set aside. In the bowl of a standing mixer, cream butter at medium speed until softened, 1 to 2 minutes. Gradually add sugar, and continue until lightened, 3 to 4 minutes, scraping down sides once or twice. Gradually add eggs, beating after each addition until batter is no longer slick, stopping once or twice to scrape down the sides, about 5 minutes. Slowly add the sifted flour mixture, alternating with the buttermilk, a little of each at a time, at low speed, beginning and ending with the flour mixture. Beat in the vanilla.

Divide the batter evenly between the prepared pans. Bake 25 minutes, and rotate the pans in the oven if needed for even browning. Continue baking until a cake tester inserted into the center of each cake comes out clean, 10 to 20 minutes more. Transfer pans to wire racks to cool. Let cool 15 minutes. Remove cakes from pans; set cakes top-side down on wire racks, and allow to cool completely, about 1 hour. (Makes two 8-inch layers)

LEMON FILLING: Sift sugar, cornstarch and salt into a medium saucepan. Gradually blend in the cold water and lemon juice. Place saucepan over medium-low and whisk until smooth. Add the eggs and 2 tablespoons butter and blend thoroughly. Stir constantly with a wooden spoon until thickened and add the boiling water. Continue stirring until the mixture reaches the desired thickness, about 2 to 3 minutes. Remove from heat and stir in the lemon peel; rub surface lightly with 1 tablespoon butter to prevent a skin from forming. Refrigerate unused portion for up to 1 week. (Makes 2 cups)

RICH CHOCOLATE FROSTING: Place chocolate and cream in heavy saucepan. Cook over low heat, stirring constantly with a rubber spatula, until combined and thickened, 20 to 25 minutes. Increase heat to medium-low, and cook, stirring, 3 minutes more. Remove from heat; stir in corn syrup. Transfer to a large metal bowl; refrigerate. Check every 15 to 20 minutes; stir until cool enough to spread, about 2 hours. Spread on cooled cake. (Makes 6 cups)

ASSEMBLY: Remove the parchment paper from each cake; reserve the one with flattest bottom surface to use for the top layer of the assembled cake. Place the other cake, top-side down, on the serving platter as the first layer. Spread a 1/2-inch thick layer lemon filling to within a 1/2-inch from the edge. Place remaining cake, top-side down, on top of the first and press down slightly. If the kitchen is warm and the lemon filling seems runny, transfer the cake to the refrigerator to firm up the filling. Ice with a rich chocolate frosting. Chill cake until frosting sets, about 10 minutes, and serve.

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