Preheat oven to 300 degrees F. Stack two matching, heavyweight, light to medium colored sheets, one inside the other (stacking two cookie sheets together keeps the bottoms of the cookies from getting too brown). Line with parchment paper or a silicone baking mat.
In a large bowl, whisk together almond flour, sugar and salt until evenly incorporated.
In a mixing bowl or the bowl of a stand mixer fitted with whisk attachment, whisk egg whites and lemon juice until they hold soft peaks.
Add beaten egg whites and almond extract to dry ingredients and stir until mixture forms a soft, sticky dough, kneading with your hands if necessary. No need to be gentle here, we're not making macarons. ;)
Lightly dust your hands with powdered sugar. Use a small cookie scoop to portion dough into 1-inch balls. Roll into a smooth ball, then roll in powdered sugar. Arrange on parchment or silicon-lined baking sheets, leaving 1 inch of space between cookies
Bake for 30 to 35 minutes until tops are cracked and bottoms are just barely golden (if you are NOT using doubled cookie sheets your cookies will brown much quicker, and will likely only need 25 minutes, so watch them closely).
If you prefer crunchier cookies you can give them an extra 5 minutes or so until the tops begin to brown too.
Remove from oven, let cool a few minutes, then transfer to wire racks to cook completely.
Cookies will keep at room tempature in an airtight bag or container, for up to 5 days.