Prepare 1/4 sheet pan by spraying non-stick spray and lining with a parchment sheet. Spray parchment and lightly flour. Set aside. Preheat oven to 350°F.

Sift almond flour into medium bowl. In the bowl of a stand mixer, add egg whites. Using whisk attachment, beat on low until surface is covered with tiny bubbles. Add cream of tartar and beat until whisk tracks are visible in eggs whites, about 2 minutes.

Begin to add sugar, spoon by spoon, allowing the sugar to completely dissolve between additions. Once all the sugar has been added, turn off mixer and scrape down sides.

Beat on medium speed for 2 minutes then bump speed to high and continue until the egg whites have reached stiff peaks and are glossy. Carefully fold in flour mixture, taking care to not deflate the eggs.

Pour into prepared 1/4 sheet pan and smooth evenly with offset spatula. Bake for 20 minutes and cool completely on top of stove.