Preheat the oven to 250°F (120°C) and line two baking sheets with parchment paper.

In a food processor, blend together 2 cups of confectioners' sugar, 10 ounces of sliced almonds, and 2 teaspoons of ground cinnamon until finely ground.

Whip the egg whites until soft peaks form, gradually adding remaining confectioners' sugar until thick and glossy.

Gently fold the almond mixture and finely grated lemon zest into the whipped egg whites until fully combined.

Roll out the dough between two sheets of parchment paper to ¼ inch thickness.

Use a 3-inch star cutter to cut out cookies and place them on the baking sheets.

Spread reserved meringue on top of each cookie and sprinkle with additional sliced almonds.

Bake for about 30 minutes until cookies are lightly golden around the edges.

Turn off the oven and leave the cookies inside for an additional 10 minutes to cool.

Cool completely on a wire rack before serving.