1. When the cakes have cooled, take each cake and trim off the top to make the top of the cake flat and trim the sides to make them straight. Slice each cake across into three pieces so that you will have six layers.
2. Set aside one of the cake bottoms to use as the top of the cake. Place the other cake bottom, bottom-side down, on your serving plate and put some pieces of waxed paper under the cake to catch the drippings.
3. Take a pastry brush, dip into the sugar syrup and brush the top of the cake slice all around to moisten it. Scoop up about 3⁄4 cup of the ganache and, using a silicone spatula, spread evenly on that layer of cake; just use enough ganache to cover the layer.
4. Add the next piece of cake, moisten with syrup, and spread another 3⁄4 cup of ganache. Repeat with all slices until you get to the reserved cake bottom for the top.
5. Place on top, bottom-side up, but do not moisten it with the sugar syrup. Use a long metal spatula to spread ganache on the top and sides of the cake so that the layers are no longer visible. Try to reserve 1 to 2 tablespoons of ganache to use for decorating the cake.
6. Heat the blade of the metal spatula in very hot or boiling water and wipe lightly with a towel to dry and then immediately slide around the sides and top of the cake to make the ganache completely smooth; you may need to reheat the blade and repeat this step a few times.
7. Place any leftover ganache in a pastry bag to make any flowers, dots, or swirls on top of the cake. You can also scrape extra chocolate with a vegetable peeler on top of the cake.
8. Store in the refrigerator until serving.