Place 1 sheet on the upper rack and bake for 15 minutes.
After 15 minutes, transfer the partially baked top sheet to the lower rack, rotating 180 degrees, and place the second sheet of dough balls on the upper rack.
Continue to bake until the cookies on lower tray just begin to darken around the edges, 10 to 12 minutes longer.
Remove the lower sheet of cookies and shift the upper sheet to the lower rack and continue to bake until the cookies begin to darken around edges, 15 to 17 minutes.
Slide the baked cookies, still on the parchment, to a wire rack and cool completely before serving.
Cool baking sheets slightly and repeat step 2 with the remaining dough balls.