Heat oven to 375° F.
Line 3 sheet pans with parchment paper.
Flip each piece of parchment over and use a permanent marker to mark 3 ½" rectangles.
Flip back over. Set aside.
Sift flour. Set aside.
With an electric mixer, beat egg yolks and ¼ cup of the sugar to ribbon stage, about 5 minutes.
Beat egg whites and cream of tartar until foamy.
Add in remaining 1/2 cup sugar, a little at a time, until incorporated.
Beat to medium stiff peaks.
Fold meringue into egg yolks one third at a time.
Fold flour into egg mixture one fourth at a time.
Spoon into piping bag.
Snip end to about a ½" opening.
Pipe onto marked parchment.
Sift powdered sugar over tops of cookies.
Immediately place in oven.
Bake for 10 minutes, or until just starting to color.
Use a thin spatula to remove from pan immediately.
Cool on wire racks.