Mix ground hazelnut kernels with the grated lemon peel and the juice of a lemon. Separate the eggs and stir the yolks with sugar until foamy, then carefully fold in the nut mixture. Beat the egg whites with a pinch of salt until stiff and fold gently under the walnut. Lay the bottom of a springform pan (26 cm) with baking paper, pour the mixture into the spring pan and smooth it out. Preheat the oven to 175 ° C and bake the cake for 45 min. Dust the cooled cake with powdered sugar.