Beat the egg white and salt for a few minutes until they reach a relatively firm peak peak consistency.
Add the confectioner's sugar and continue to beat/whisk until the mixture is well combined and glossy.
Add the almond meal/flour, lemon juice and zest, and vanilla sugar if using. Mix everything together with a spatula so that it is well combined. Bring the dough together into a flattened ball, and ideally wrap it and refrigerate around 30 minutes to an hour to help it firm up (you can roll straight away but it's likely to be more sticky).
Preheat the oven to 275F/135C and prepare one or two baking sheets with parchment or silicone baking mats.
Place a silicone baking mat on a work surface or cut a piece of waxed paper to line an area. Sprinkle the mat/paper with a little confectioner's sugar then place the chilled dough on top, slightly flattened.
Roll out the dough to roughly 0.4in (1cm) thick. If it's sticky, either place parchment between the dough and rolling pin or dust rolling pin with confectioner's sugar. Use a crescent moon shaped cutter, or cut circles and overlap to make crescents as in photos above. Carefully transfer the cut cookies to the prepared baking sheets. To help stop the cutter sticking, try dipping the cutter in confectioner's sugar now and then.
Once you have cut cookies from the dough, bring back extra dough into a ball and roll out again to cut additional cookies.
Bake the cookies for approximately 30 minutes until the top of the cookie looks dry and the edges are only just starting to show a little color. Remove the cookies from the oven and allow to cool completely.
Once cool, mix together the confectioner's sugar and lemon juice for the glaze. It should be a relatively stiff mixture, but still spreadable, so add more sugar/lemon as needed. Use a teaspoon to spread the glaze over the top of each cookie - ideally you have an even layer over the top but without dripping down. Place cookies on cooling rack to dry before storing in an airtight container or serving.
Video
Notes
Cookies will keep, stored in an airtight container at room temperature, for approximately 2 weeks, becoming slightly more chewy and softer over time.