Adapted from a recipe from Babbo.
Preheat the oven to 325 degrees. Butter and flour an 8-inch cake pan.
In the bowl of an electric mixer, cream together the butter and sugar for 2 - 3 minutes, until fluffy and light in color. One at a time, beat in the eggs and vanilla.
In a separate bowl, whisk together the flours, hazelnuts, salt and baking powder. Scrape down the sides of the bowl and beat the dry ingredients into the batter. Fold in the chocolate chips.
Spread the batter into the pan and smooth the top. Bake for 30-35 minutes, until a cake tester inserted into the cake comes out clean. Allow the cake to cool in the pan for 10 - 15 minutes before gently removing.
Dust with cocoa powder and serve.