In a larger bowl, beat the egg whites (using a hand mixer) until stiff peaks form. Slowly add the icing sugar and combine well. Remove 8 tbsp of the egg white mixture and set aside for the frosting.
Carefully add the ground almonds and cinnamon. If desired, stir in the optional Amaretto. Mix well. If the dough is too sticky, add more ground almonds/ icing sugar. If the dough is too dry, add more egg whites.
Place the dough in the fridge and chill for about 30 minutes.
Preheat the oven to 150 C (302 F) and line a baking sheet with parchment paper.
Lightly sprinkle a non-stick surface with icing sugar. Roll out dough (about 1 cm thick). Dust a star-shaped cookie cutter with icing sugar and cut out shapes.
Using a pastry brush, spread the frosting (that you set aside earlier) on top of each cookie.
Transfer cookies onto the prepared baking sheet and bake on the lower rack for about 10-15 minutes OR until the top begins to turn slightly (!) golden (you will need to watch them carefully!). Take them out immediately as they should stay light in colour. Do NOT use the fan as we want the frosting to stay white.
Remove the cookies from the oven and let cool completely.
Store your Cinnamon Stars in an airtight container for up to four weeks.
*Reduce to three egg whites if you are using large or jumbo eggs.