To make the cake:
Preheat oven to 350degreesF with the oven rack in the middle. Grease a 13x18-inch baking sheet and line it with parchment paper.
Shave the chocolate using a box grater or the grater attachment on your food processor. It needs to be fine flecks of chocolate in order to blend well into the cake.
Cream the butter, sugar and yolks together, using the paddle attachment on your stand mixer, on medium speed, until they are light and fluffy, about 3 minutes.
Add the shaved chocolate and almond meal to the butter mixture and mix on low speed until it is evenly distributed. Turn the speed up to medium and mix for 1 more minute.
In a clean mixing bowl whip the egg whites on medium high until they are at soft peaks, about 3 minutes, but be sure to watch them carefully. If the egg whites are over whipped and curdled looking they will be difficult to fold into the chocolate mixture. Mix a third of the whites into the chocolate mixture. This will lighten up the chocolate mixture so you can fold the rest of the whites in more easily. Add half of the remaining whites and gently fold them into the chocolate. Repeat with the remaining whites. Pour the batter onto the prepared pan and use a spatula to smooth the mixture out, making sure it is very even.
Bake for about 20 minutes or until a tester comes out clean.
Allow the cake to cool in the pan completely on a cake rack.
Once the cake is cool, run a knife around the edge to loosen it. Invert the cake onto the back of another baking sheet, covered with parchment or a cutting board covered in parchment. Peel the parchment off of what is now the top of the cake.
Pour 1/3 of the ganche over the cooled cake. Spread the ganache evenly over the surface. Refrigerate the cake and allow the ganache to cool completely.
Cut the cake into 3 equal pieces, cutting along the long side of the cake.
Stack the 3 layers together. Trim the sides so they are perfectly smooth and then cut the cake in half.
Stack the 2 pieces to create a cube. Place the cake on a cooling rack set over a baking pan, which will catch the dripping ganche. Pour the remaining ganche slowly over the top of the cake. It needs to be cool enough that the ganache clings to the cake and doesn't just drip off. You may have to go over it a few times to make sure the whole thing is covered smoothly.
You can use the leftover ganache, once it has set firm at room temperature, to pipe a design along the bottom of the cake after you have placed it on a serving dish.
Decorate with berries and edible flowers.
To make the ganache:
In a large saucepan bring the cream substitute to a gentle simmer. Turn off the heat and add the finely chopped chocolate. Swirl the chocolate in the pan to make sure the liquid covers it all and allow it to sit for 3 minutes. Gently stir the ganache with a rubber spatula until it is completely smooth. You do not want to whisk the mixture or you will get air bubbles in the ganache. Let the ganache sit for 15 minutes to cool slightly.