Lightly coat two 15x10-inch pans with non-stick spray, then cover with baking paper (try to avoid wrinkles). Set pans aside and preheat oven to 350 degrees.
In a bowl sift together flour, baking powder, salt and first amount of sugar.
In separate bowl, combine vegetable oil, egg yolks, water, lemon zest and vanilla extract.
Mix the liquid mixture into the dry mixture, then blend the batter with a hand blender until very smooth and light in color.
Next make an Italian meringue. Begin by cooking the sugar; in a small bowl combine the second amount of sugar with enough water to make a loose paste. Pour this loose sugar paste into a small saucepot avoiding splashing the sides. Cover and cook sugar on a high heat until it reaches 238 degrees. Remove pot from heat and begin whipping the egg whites in an electric mixer on medium high speed. Whip egg whites until soft peaks form then pour sugar syrup into mixer in a slow steady stream. After sugar is added continue to whip until meringue becomes stiff and shiny.
Fold meringue into batter. Divide finished mixture into the prepared cake pans and spread evenly. Bake for approximately 10 minutes. When tested for doneness the center of the cake should have the same bounce as the sides. Baked cakes can be stored in the refrigerator until ready to assemble.
Chocolate Pudding Filling [Day 1]
Combine milk, cream and salt in a saucepot. Bring to a simmer over medium high heat.
In a large bowl, whisk together sugar and cornstarch until it is lump free. Add egg yolks into sugar mixture and stir again until lump free.
When milk mixture is at a simmer slowly add into yolk mixture. Pour milk and egg mixture into pot and return to the stove. Cook on medium heat until mixture has boiled for 5 minutes. Stir constantly. Remove from heat.
In an electric mixing bowl, add chopped bittersweet chocolate, then pour cooked custard on top. Mix on low speed with a paddle attachment until mixture is nearly room temperature. Pour into a shallow pan, cover with plastic wrap and refrigerate overnight.
Chocolate Ganache [Day 1]
Combine cream, sugar and corn syrup into a saucepot and bring to 180 degrees.
Chop chocolate into small pieces and place into a small bowl. Pour hot cream mixture onto chocolate and let sit for 5 minutes to melt before stirring. Stir until smooth.
Add room temperature butter. Emulsify mixture with a hand blender. Mixture should be smooth and glossy. Cover with plastic and place in a cool (65 degrees) spot overnight.
Simple Syrup and Cake Assembly [Day 2]
Combine sugar, water, lemon zest and scraped vanilla bean in a pot. Bring to a boil. Remove from heat and let steep for 20 minutes. Strain and cool before using.
To assemble cake, first invert sheet cake from pan and peel away baking paper. Before inverting cover the top of cake with a fresh sheet of baking paper. Next cut each sheet cake into 3 equally sized pieces approximately 5 inches wide x 10” long.
Start by putting the first layer onto a cake board. Brush on simple syrup then spread on a layer of chocolate pudding. The pudding may need to be stirred smooth before using. Each layer of pudding should be equal in height to each layer of cake.
Repeat process until all the cake is used. There should be 5 layers of pudding and 6 layers of cake.
After cake is an assembled, smooth the sides and let chill in refrigerator for at least an hour before glazing.
To glaze cake, melt ganache over a pot of simmering water. Reserve 1 cup from melting to use for piping decorative shells. Place assembled cake onto a cake rack. Pour melted ganache over cake to completely cover. Allow excess ganache to drip off and transfer the cake to a cake plate. Refrigerate until ganache hardens before add finishing touches. At this point the cake can be decorating with the ganache reserved in a piping bag and fresh berries.