Pre-heat oven to 170 deg C (335 - 340 deg F). Place rack in the lowest part of the oven.

In a mixing bowl, mix egg yolks, sugar, salt, vegetable oil and milk until well combined. Sift in the flour, ground cinnamon and baking powder. Add the ground hazelnut. Mix till well combined.

Using an electric or hand-held mixer, whisk or whip egg whites on medium speed (speed 4 on my Kitchen Aid mixer) until it just starts to foam. Add the cream of tartar. While whipping, add sugar in a slow, continuous steady stream. Whip until the meringue reaches the stiff peak stage (be careful not to over-whip).

Scoop 1/4 of the meringue and add to the egg yolk-flour mixture. Fold lightly until just incorporated. Add the remaining meringue and fold lightly until well incorporated. Add half of the mixed nuts and fold in until just combined.

Pour batter into a 20-cm ungreased chiffon pan. Gently tap the pan on the counter top a couple of times, and run a flat blade in an 'S' pattern around the batter to eliminate air pockets. Level the surface evenly, and sprinkle the remaining nuts on top.

Bake at the lowest rack in the oven for 35 to 40 minutes, or until a skewer inserted in between the side and the funnel of the chiffon pan, emerges free of batter. Remove from the oven, and immediately invert the pan onto a cooling rack. Let cool for at least 30 minutes, before loosening the cake.

To loosen the cake, turn it up again so that the surface of the cake is now facing up. Insert a flat blade in between the cake and pan and run the blade around the circumference of the pan, pressing against the pan as much as possible. Then invert the pan again so that the bottom of the pan is now facing up. Gently tap or push the pan's base to loosen the cake from the sides of the pan. Then run the blade between the base and the bottom of the cake to loosen it from the base of the pan.