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