Preheat the oven at 350 F
On a baking sheet spread the hazelnut evenly and toast them in the oven for 15 minutes.
Once the skin on the hazelnuts starts peeling, around 15 minutes, remove from the oven and wrap the nut into a kitchen towel and let them steam for 5 minutes.
Next, vigorously rub them to get in the towel to remove the skin.
Once the skin is almost gone from the nuts, return them to the baking sheet and bake for another 12 minutes. They would golden brown in color.
Let them cool while you brown the butter
Place 1/2 pound butter in a medium sauce pan. Slice the vanilla bean and using a paring knife scrape the seeds and pulp and add it to the butter.
Add vanilla pod to the pan as well and cook the butter and vanilla on a medium low heat until it is brown. Around 6 minutes. Stir and scrape frequently.
Remove the vanilla pod and let the butter cool down in a heat proof bowl.
Grease a 10 inch round pan with melter butter and line with parchment paper. Keep aside.
Grind the hazelnuts with the powdered sugar in a food processor until they’re finely ground. Add the flour and pulse to combine. Transfer to a large bowl.
Place the egg whites in the bowl of a stand mixer fitted with the whisk attachment. Whisk on a medium speed until the whites are foamy. Add the granulated sugar and mix on high speed for 5 minutes, until the mixture forms very stiff peaks.
Transfer the whites to a large mixing bowl.
Alternately fold the dry ingredients and the brown butter into the egg whites, a third of a time.
Pour the batter into the prepared cake pan, and bake for 40 to 50 minutes. Until the cake tester comes out clean.
Let the cake cool on a wire rack for 30 minutes.
Run a knife around the inside edge of the pan, peel off the paper, and turn the cake over onto a serving platter.
