Vanilla bean cake layers baked on a graham cracker crust with vanilla bean custard and vanilla bean buttercream.
Preheat your oven to 375 degrees F. Spray three 8-inch or four 6-inch round cake pans with non-stick spray and then line with parchment. Spray again. Set aside.
In a medium sized bowl combine the graham cracker crumbs, melted butter, sugar and coffee granules, if using. Stir until all the graham cracker crumbs are damped by the melted butter.
Divide evenly between the three pans (about 8 ounces in each 8-inch or 6 ounces in each 6-inch) and press down firmly with your hand or the back of a spoon.
Bake for 6-8 minutes, until golden brown. Let cool while you make the cake batter.
Preheat your oven to 325 degrees F.
In a medium sized mixing bowl, whisk together the cake flour, baking powder and salt. Set aside.
In the bowl of an electric mixer, fitted with the paddle attachment, cream the butter and the sugar for two minutes on medium-high speed.
Scrape down the sides of the bowl and begin to add the egg whites on medium speed, scraping down the sides and bottom of the bowl between addition.
Add the sour cream and vanilla bean paste and beat until incorporated, about one minute.
With the mixer on low speed, add 1/3 of the flour mixture, followed by 1/2 cup of the buttermilk. Repeat the additions, 1/3 cup flour mixture, 1/2 cup buttermilk and the final 1/3 cup flour mixture. Only mix until the flour mixture is incorporated, about 30 seconds. Scrape down the sides and bottom of the bowl and mix again for another 20 to 30 seconds on low.
Pour about 18 ounces of cake batter into each of the three 8-inch cake pans or 13 ounces in each of the 6-inch pans and bake for 28-30 minutes - until a toothpick inserted into the center of the cake comes out with a few moist crumbs on it. Let cool in the pans for about 15 minutes and then invert onto a wire rack to cool completely. (Tip: spray your wire cooling racks with nonstick spray).
Preheat your oven to 300 degrees F. Place an 8"x8" baking pan in a 9"x13" baking pan. You'll be adding water to the larger pan later to create a bath for the custard to cook in - so you're looking for a pan that is larger than the baking pan that you'll have the custard in.
In a medium saucepan, combine 1 cup of the heavy cream with the vanilla bean paste and the sugar. Turn the stove to medium heat and bring the mixture to a boil, stirring often to dissolve the sugar. Once the mixture starts to boil, remove from heat and cover with a lid. Let sit for about 5 to 10 minutes.
After the cream has steeped, stir in the remaining 1 cup of heavy cream.
In a small mixing bowl, whisk the egg yolks. Slowly add about 1/4 cup of the heavy cream mixture to the egg yolks, whisking continuously while you do so. This is how you temper the eggs. Once the eggs are tempered, slowly add the egg mixture to the remaining cream, stirring continuously while doing so.
Strain the custard through a mesh strainer and then pour the strained custard into your 8"x8" baking pan. Carefully pour hot water into the larger baking pan that the small baking pan is sitting in. You want enough water to go about half way up the side of the baking dish.
Bake the custard for about 45 to 50 minutes. The center should be barely set. Let cool at room temperature for 2 hours and then cover with plastic wrap and refrigerate for at least 4 hours before using. I think the custard is best made one or two days before you're ready to assemble the cake.
In the bowl of an electric mixer, fitted with the paddle attachment, beat the butter for about 2 minutes, until light and fluffy and pale in color.
With the mixer on slow, gradually add the powdered sugar, followed by the heavy cream, vanilla bean paste and pinch of salt.
Once all of the ingredients are combined, turn the mixer to medium-high and beat for about 3 to 5 minutes. Scrape down the sides of the bowl and beat for a couple minutes more.
Before using the buttercream, make sure to beat it by hand with a wooden spoon or large spatula to help push out the air pockets.
Level each cake layer, if needed, and then place the first cake layer, graham cracker side down, on a cake board.
Using a piping bag, pipe a rim of buttercream around the edge of the cake.
Fill the center of this area with 1 cup of the custard.
Place the second cake layer on top of the filling and repeat steps 2 and 3.
Place the final cake layer, graham cracker side down, on the second layer of filling. Carefully apply a thin layer of buttercream around the entire cake. This is the crumb coat. Freeze the crumb coated cake for about 15 minutes.
Once the crumb coat is set, continue frosting the cake with the remaining buttercream.
OPTIONAL: Freeze the cake for another 15 to 20 minutes. Sprinkle a layer of granulated sugar over the top of the cake and use a kitchen torch to caramelize the sugar. Serve right away or refrigerate, covered, until you're ready to serve.