Mix finely ground cashews and set aside
Beat 8 egg whites at medium speed, then high speed until soft peaks form
Gradually add 1 cup sugar while beating until meringue reaches ribbon stage and doubles in volume
Spread meringue onto parchment paper in a pan using an offset spatula, ensuring it is level
Bake meringue at 300°F for approximately 45 minutes until dry
Make French buttercream by heating water and 1 cup sugar to 115°C
Beat 8 egg yolks until uniform bubbles form
Slowly add hot syrup to egg yolks in a thin stream while mixing on high speed
Let mixture cool completely
Add 2 cups softened unsalted butter gradually to cooled egg yolk mixture
Add 1 tsp vanilla and mix until uniform in color with no unmixed butter
Cool baked meringue for a few minutes, then run a knife around the sides to release from pan
Remove parchment paper and cut meringue into 4 layers
Spread French buttercream between meringue layers using an offset spatula without lifting
Spread thin layer of buttercream on top
Refrigerate for 5 minutes
Garnish with 1 cup coarsely chopped cashews on top
