Whisk the egg whites with just a drop of lemon juice until foamy, a minute or two.
Add the powdered sugar, almond flour, extracts and orange zest and mix well until the dough comes together. Cover and refrigerate overnight or at least 12 hours.
Preheat the oven to 320°F (160°C). Meanwhile, lightly dust your work surface with powdered sugar. Roll the dough into a log, about 1 inch in diameter. If you find the dough is too sticky to handle, the egg whites may have been a little big. Add a touch of rice flour to bind things together.
Slice even rounds, about 20-25.
Shape the dough with your hands into an oval shape, with slightly pointed ends, about ⅓ inch (1 cm) thick. If the dough is sticking, slightly wet your hands. Place the cookies on a parchment lined cookie sheet, spaced about 1.5 inches (4 cm) apart.
Lightly wet your hands with water and ever so lightly pat each cookie. Gently roll the shaped cooking in the remaining powdered sugar (or sift it directly onto the cookies already placed on the baking sheet) and return to the baking sheet or generously sift the powdered sugar directly on top of the cookies.
Bake for about 18-20 minutes. They will still be soft and moist and seem undercooked but they will set to the correct consistency when cool.