Combine the almond flour, sugar, ¼ cup of the powdered sugar and zest. Set aside.
In a small bowl, beat egg whites until soft peaks form. Gently fold into almond mixture, once smooth fold in remaining ingredients.
Add remaining ¼ cup of powdered sugar into a small dish. Use a small cookie scoop (2 teaspoons' full) and drop the ball of cookie dough right into the powdered sugar, rolling it around to cover completely. Use a fork to lift and place it on a parchment lined baking sheet.
Pinch the ends of the ball, and slightly flatten top to create a diamond shape. Let cookies sit uncovered on the counter for 2 hours to firm and dry up a little, this will prevent them from spreading too much while baking.
Bake at 325°F for 12 minutes, or just until edges begin to brown.
Once cool, dust with (more) powdered sugar if desired. Store in an airtight container.