Grease and line a 9-inch cake pan.
Blitz walnuts in a food processor until coarsely ground.
Separate egg whites and yolks from the eggs.
Add ½ cup sugar to egg whites and beat until stiff peaks form.
Add another ½ cup sugar to egg yolks and beat until pale and doubled in size.
Stir ground walnuts into the yolk mixture until combined.
Fold in half of the egg whites gently, then fold in the remaining egg whites until no visible egg whites remain.
Pour the mixture into the cake pan and bake at 350°F (175°C) for 30-35 minutes.
Let cool completely in the pan.
Run a knife around the edges and remove the cake from the pan.
Dust with powdered sugar before serving if desired.
