Preheat the oven to 350 degrees F. Place an oven rack in the middle position. Lightly spray the bottom of 3 8-inch cake pans with baking spray and then cover them with parchment rounds. Set aside.
Whisk together the flour, cornstarch, baking powder, salt and cardamom in a medium bowl.
Slice 4 vanilla beans in half lengthwise with a small paring knife. Use the dull side of the knife to scrape out all of the seeds. Add the seeds to the dry ingredients and separate any large clumps.
In a separate small bowl, combine the half and half, brandy and vanilla extract.
In a stand mixer with the paddle attachment, cream the butter and sugar together on medium high speed for several minutes. On low speed, add the eggs, one at a time, allowing each egg to incorporate before adding the next. Scrape down the sides of the bowl. With the mixer still on low speed, quickly alternate between adding the dry and liquid ingredients (ending with the dry) until just combined. Scrape down the sides well, making sure to reach the bottom of the bowl.
Distribute the batter evenly between the 3 prepared cake pans, using a spatula to even out the tops.
Bake until the a toothpick comes out of the center of each cake clean, approximately 30-35 minutes. Allow the cakes to cool completely in the pan before removing.
Prepare the frosting:
Add sugar, water and corn syrup to a medium sized sauce pot. Cover and turn the heat to high. Once the liquid begins to simmer and steam has developed, remove the cover (this helps prevent crystallization). Using a candy thermometer, cook the sugar to the soft boil stage, 235-240 degrees F.
While the sugar is cooking, whisk the egg whites on high in a stand mixer with the whisk attachment until a soft peak has formed.
Turn the mixer speed down to medium low and very slowly pour the syrup down the side of the bowl into the egg whites. Don’t pour the hot syrup directly into the meringue.
Once the syrup is completely incorporated, turn the speed to high and allow the meringue to continue to form a stiff peak while cooling down. Mix on high until the meringue has reached room temperature. To speed up this 15-20 minute process, ice packs can be placed around the bowl.
While the meringue is cooling, scrape the seeds from the remaining two vanilla beans.
Once the meringue is at room temperature, slowly begin incorporating the soft butter on medium speed. Once all of the butter has been incorporated, turn the mixer speed up to high and very slowly add the vanilla bean seeds, vanilla extract and cardamom.
Assemble the layers:
Place the first layer of cake on a revolving cake stand and remove the parchment paper. Placing a cardboard round below the cake is optional but will make transporting the cake easier after it is assembled.
Spread approximately one cup of buttercream on the cake and spread it around evenly with an offset spatula. Add more buttercream as needed to reached the desired thickness. Repeat with the second and third layer (don't forget to remove the parchment each time). Use an offset spatula to apply a thin layer of frosting to the side and top of the cake. Chill in the refrigerator for 30 minutes to set this first layer of buttercream. Cover the entire cake with a final layer of frosting.
Cake is best when served at room temperature.
If you don't consume alcohol, substitute half-and-half for the brandy (or 2 tablespoons half-and-half + 2 tablespoons vanilla extract).To get clean slices when cutting the cake, use a long, sharp knife. Run it under hot water, wipe it dry and immediately cut one slice in a straight down, non-sawing motion. Don’t pull the knife up, pull it straight out toward you. Then repeat the process for the other side, starting with the hot water.Also, Italian meringue buttercream can be a finicky thing. I've run into issues with it breaking in the past if the environment isn't perfect. Read my article with tips on how to solve common buttercream issues.