Combine hazelnuts and baking powder. Set aside.
In a large bowl, whip the egg yolks with the sugar until pale yellow in color. Then add in the hazelnut mixture.
In another bowl, beat the egg whites until stiff.
Quickly fold 1/3 of the egg whites into the yolk mixture, then add the remaining whites and fold in until no streaks remain.
Pour into a greased 9" springform, and bake at 325°F for 60 to 75 minutes, or until top of cake springs back when lightly tapped.
When cake is cool, slice horizontally into 3 layers. Whip cream until stiff peaks form then spread over the layers of the cake, and stack. Continue spreading whipping cream on sides and top of cake.
Garnish with chopped hazelnuts if desired.