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• In a medium bowl, sift together the almond flour, 1 cup (120g) powdered sugar, and baking powder.
• In the bowl of a stand mixer fitted with a whisk attachment, or in a large bowl with which an electric hand mixer is to be used, beat the egg whites, salt, and lemon juice to stiff peaks. Fold in the lemon zest.
• In small additions, sift the dry ingredients directly into the egg white and lemon mixture, folding thoroughly after each addition. Deflation of the egg whites is to be expected. Add the vanilla and almond extract midway through this process.
• Pinch off 11/2 tbsp of dough (#60 cookie scoop) and roll in the hand to form balls. Roll thoroughly in the remaining 1/2 cup (60g) of powdered sugar and place on a parchment-lined baking sheet.
• Leave the formed dough to dry on the baking sheet for an hour, before lightly flattening each ball with two fingers. A cookie stamp, or a glass with a decorative indentation may also be used.
• Preheat the oven to 325ºF (165ºC).
• Bake for 20 to 25 minutes.
• Cool briefly on the baking sheet before carefully transferring to a wire rack to cool completely.