Preheat oven at 375 F degrees.
Grease a 9 inch cake pan with baking spray or butter and flour. Set Aside.
Grind the hazelnuts in a food processor or high speed blender.
Mix the hazelnuts with sugar, flour and vanilla baking powder.
Add the egg yolks and butter and blend thoroughly.
Whip the egg whites with the salt at stiff peak.
Gently fold in the whipped egg whites into the hazelnut mixture.
Bake for 35 minutes.
Allow to cool completely in its pan.
Sprinkle with powdered sugar before serving.