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

In a food processor, blend ½ cup of confectioners' sugar, 10 ounces of sliced almonds, and 1¼ teaspoons of ground cinnamon until fine.

Whip 3 large egg whites on high speed until soft peaks form, then gradually add 1¾ cups of confectioners' sugar until thick and glossy.

Reserve ⅔ cup of meringue for topping, then fold the almond mixture and 2 teaspoons of lemon zest into the remaining egg whites to form a stiff dough.

Roll the dough between two sheets of parchment paper to about ¼-inch thickness and cut out cookies with a star-shaped cookie cutter.

Spread reserved meringue over each cookie and sprinkle with additional almond slices if desired.

Bake for about 30 minutes or until the bottoms are golden brown and the meringue is set.

Turn off the oven and let the cookies cool inside for an additional 10 minutes, then transfer to a wire rack to cool completely.