Mix almonds with the flour and 100 grams (approximately 3 ounces) sugar. Pulse in a food processor into a fine powder and transfer to a bowl. Stir in baking powder.
Beat egg whites with salt using an immersion blender until stiff. Sprinkle in remaining sugar. Beat until mixture is cut resistant and glossy. Fold in almond mixture and lemon zest.
Roll dough between plastic wrap until 3-4 cm (approximately 1 1/2 in) thick rolls form. Roll in flour and then cut into slices. Spread on a baking sheet lined with parchment paper and let rest for 30 minutes.
Meanwhile, preheat oven to 120°C (approximately 250°F).
Bake for 18-20 minutes. Dust with powdered sugar while still hot. Cool and serve.