To make the cookie dough, place softened butter, granulated sugar, and ground cinnamon in the bowl of a stand mixer and mix. Add egg, hazelnut, and almond meal and mix again.

Add the sifted all-purpose flour and mix to combine. Remove the cookie dough from the bowl and form a ball.

Roll the dough out with a rolling pin between two sheets of parchment paper (sprinkled with icing sugar) to the thickness of 0.4 inch (1 cm) and refrigerate for 1 hour.

To make the white royal icing, whisk the egg white with icing sugar and 3 - 4 drops of lemon juice using an electric mixer.

Take the cookie dough out of the fridge and spread a thin layer of royal icing with a bent spatula. Chill the dough in the refrigerator for 30 minutes or in the freezer for 15 minutes.

Preheat oven to 300°F (150°C). Cut out cookie stars with a 2-inch (5 cm) star-shaped cookie cutter by dipping it in hot water and drying it out between cutouts. Remove cookies by pushing them underneath, and arrange them on a baking sheet covered with parchment.

Bake cookies in the middle of the preheated oven for 12 to 15 minutes. They must be baked, but the royal icing must not be colored. Remove cookies from the oven and let them cool down on a wire rack.