Preheat your oven to 150 °C / 300 °F. Place the rack in the middle of the oven. Line a baking sheet with parchment paper.
dry and wet ingredients
Add powdered sugar to a large bowl. Save about a tablespoon of powdered sugar for egg whites. Add almond flour and salt, and stir to combine. Beat the egg whites with a tablespoon of powdered sugar and freshly grated lemon zest in a smaller bowl. Use a hand whisk or an electric mixer and whisk until soft peaks form (the mixture should be foamy and light).
shape the cookies
Add the egg white mixture to the almond mixture. Using a spatula, stir to form a cookie dough. Cut the dough in half, and shape each half into a long rope 3 cm (1-inch) in diameter. Cut rope into small pieces 1 cm (1/2-inch) in diameter. Place each cookie on a prepared baking sheet. Using your hand, gently push down.
Don't overcrowd the cookies on the baking sheet. Generously sprinkle with powdered sugar. Place in the preheated oven and bake for 18 - 20 minutes at 150 °C / 300 °F or until the cookies are golden-brown and the exterior cracks slightly. Remove from the oven and leave to cool completely, then transfer to a cookie jar.