Preheat the oven to 350F. Lightly grease the half sheet pan. Lay a sheet of parchment on the pan and lightly grease the parchment. Set aside

In the electric mixer with the paddle attachment, cream together the butter and sugar until smooth. Add the eggs one at at time while scraping the bowl in between each addition. Add the vanilla extract.

Combine all the dries and add them to the mixer on low speed while alternating with the milk. Give the batter a good final scrape at the end before pouring it into the prepared sheet pan.  Make sure to spread the batter out evenly with an off set spatula or your cake will not bake evenly in the oven. Bake at 350F for 15-20 minutes until golden brown and springs back when pressed. Let it cool completely before removing from the pan.

Prepare the filling by whipping the heavy cream on medium speed. Add the powdered sugar and whip until soft peaks form.  Fold in the blackberries. If the berries are quite large, make sure to slice them in half before folding it into the cream. Place it in the refrigerator until the cake is ready.

To prepare the buttercream, soften the butter in the electric mixer until soft and smooth. Add the sifted powdered sugar and black sesame powder. Mix until smooth. Add the milk to the buttercream if it's too dry. Bag 1/3 of the buttercream in a piping bag with a large round tip.

To unmold the cake, release the cake from the sides of the pan with a pairing knife. Place a sheet of parchment on the top and flip it over on a large cutting board or work surface. Remove the parchment baked onto the bottom of the cake. Slice the cake in half. It should now look like two pages in a book. Trim both sheets of cake to look like a tombstone. If you can not do this free hand, sketch or print out a template as a guideline.

Take on of the sheet cakes and pipe the buttercream around the edge of the cake. Pour the blackberry cream mixture into the center and smooth out with an offset spatula. Top it with the other half of the cake and press down gently.  Cover the cake evenly with the rest of the buttercream.

Write out "Sir Nicholas di Mimsy-Porpinton Died 31st October 1492" on the cake with black writing icing. Store the cake in the refrigerator and temper it 30 minutes prior to serving.