Preheat oven to 325 ยบ F
Butter and Flour a standard sized Bundt Pan... set aside
In a mixing bowl, beat the butter and sugar at medium high speed until light and fluffy, around 4 to 5 minutes. Lower the mixing speed, then add the eggs, one at a time. Beat between each one. Scrape down the bowl. Add Vanilla extract, beat in.
Combine the flour and baking powder, then, with mixer on low, add to the butter mixture. Scrape down the sides of the bowl, and continue to beat until the flour is completely mixed in.
Either by hand with a spatula, or with a stand mixer on low, add the ground hazelnuts and chocolate. Stir until combined. (Don't miss the pockets of nuts at the bottom, you want to mix it all together evenly).
Fill the prepared Bundt pan with the cake batter. It will be a little stiff, this is right. Smooth the top.
Bake for 55 to 60 minutes.
Check at 55 by sticking a toothpick in, it should come out clean (except for a possible smear of melted chocolate)
Remove the cake from the oven and leave to rest on a cooling rack for 10 minutes. This is important, it MUST sit for 10 minutes before inverting, or it will stick)
Flip the cake out of the pan, then let cool completely
Sprinkle with powdered sugar for serving.