With a rotary grater, finely grind the hazelnuts. (Or process them with 2 Tbs. of the flour in a food processor until finely ground.) In a large bowl, whisk the ground hazelnuts, all-purpose and cake flours, baking powder, baking soda, and table salt until well combined. In another bowl, whisk the buttermilk, oil, eggs, sugar and vanilla until well combined. With a very open whisk or a rubber spatula, lightly stir the wet ingredients into the dry until just combined (small lumps in the batter are fine). Let the batter rest for at least 20 minutes (and up to 2 hours in the refrigerator). Cook the waffles according to your waffle iron manufacturer’s instructions. In a Belgian waffle maker, the waffles have a tender interior; in a standard waffle maker, they’ll be crisper.