Preheat the oven to 350°F/180°C .

Peel the hard boiled eggs, cut in half and remove the yolks. Mash the egg yolks with a fork, and mix with the sugar, salt, cinnamon and lemon zest. Add the flour and butter, and knead everything together. Chill the dough for 30 minutes.

Place the dough on a floured surface, and roll out to slightly less than ¼ inch thick. With a cookie cutter or other instrument, cut small circles out of the dough and place on a greased baking sheet.

For the topping, beat the egg whites until stiff and stir in the sugar. Coat the dough circles with the egg white mixture. Cut the hazelnuts in half, placing a half into the egg foam on each cookie.

Bake in a preheated oven for about 20 minutes.