Begin by sifting the almond flour and pistachio flour into a large mixing bowl to remove any lumps and aerate the mixture. Prepare egg whites, lemon juice, and pistachio extract.
Using an electric mixer or whisk, beat the egg whites with the lemon juice until soft peaks form, stabilizing the whites.
Add granulated sugar and salt to the sifted nut flours. Mix thoroughly. Gradually fold in the beaten egg whites gently to form a sticky dough without overmixing.
Stir in the pistachio extract gently to enhance the nutty aroma and flavor.
Dust hands with confectioners’ sugar, scoop tablespoon-sized portions of dough, roll into balls, then roll in confectioners’ sugar to coat.
Place cookie balls on a parchment-lined baking sheet about 2 inches apart. Bake at 325°F (163°C) for 18–20 minutes until puffed with crackled tops but not browned.
Cool cookies on the baking sheet for 5 minutes, then transfer to a cooling rack to cool completely before serving.