Line the same square pan (from the matcha sponge) with plastic wrap.
Press the pistachio feuilletine into the bottom of the pan, making sure that it is spread evenly. Use the bottom of a spoon to do this.
Pour the matcha mousse mixture on top of the feuilletine and refrigerate until set. As I was working to a tight time limit, I popped mine into the freezer for about 30 minutes.
Spread an even layer of the white chocolate buttercream onto the set mousse gently.
Place the matcha sponge over the white chocolate buttercream layer. Cover the top of the cake with more plastic wrap and refrigerate for another 30 minutes to set.
To remove the cake from the cake pan, we flipped the cake onto a chopping board (to remove the bottom plastic wrap) before flipping it onto the slate where we trimmed the sides of the cake.
Spread the matcha ganache layer over the top of the cake evenly. As I only wanted the glaze to be on the top, this meant that I had to be extra careful. (Unfortunately, during the car ride to Michele's house, this meant the glaze spilled a bit over the sides.)
Decorate as you wish. I used dehydrated strawberries and crushed them to a fine powder before sprinkling at the corner of the cake. Topped with fresh edible flowers from the garden, the cake is ready to be served.