Preheat oven to 350°F and line a baking sheet with a piece of parchment paper. In a medium mixing bowl, stir together the almond flour, granulated sugar, lemon zest and salt. Set aside. In a large mixing bowl, beat the egg whites at medium speed using an electric hand mixer or stand mixer until soft peaks form. Stir in the lemon extract and then stir in the flour mixture. It'll be a thick dough. Roll into balls, about 1 1/2 tablespoons in size, and roll in the powdered sugar. Place the cookies 2” apart on the prepared baking sheet. Bake for 15-17 minutes or until the tops have crackled and the bottoms of the cookies have lightly browned. Let cool completely on the baking sheet. Store in an airtight container for up to 3 days.