Preheat your oven to 250°F (120°C) and line two baking sheets with silicone liners or parchment paper.

In a food processor, combine ½ cup of confectioners' sugar, 10 ounces of sliced almonds, and 1 tablespoon of ground cinnamon. Pulse until fine.

Whip 4 large egg whites on high speed until soft peaks form. Gradually add the remaining 1 cup of confectioners' sugar to create a thick meringue. Reserve ⅔ cup for topping.

Fold the almond mixture and finely grated zest of 1 lemon into the whipped egg whites until a stiff dough forms.

Roll out the dough between two sheets of parchment paper to about ¼-inch thickness. Cut out star shapes and transfer to the prepared baking sheets.

Spread a thin layer of reserved meringue over each star-shaped cookie and optionally sprinkle sliced almonds on top.

Bake for approximately 30 minutes until they feel firm and meringue is set.

Turn off the oven and crack the door, leaving the cookies inside to dry for about 10 minutes.