Preheat the oven to 350 degrees F.
In a clean bowl of an electric mixer using the whisk attachment, whip the egg whites on medium speed until frothy. Increase to high speed and slowly add the remaining 1/2 cup sugar. Whip the egg whites until stiff and then fold them into the reserved batter. Gently spread the batter in the prepared baking tray. Bake until the cake is golden brown and springs back lightly when touched, about 20 to 25 minutes.
Cool the cake in the pan. Remove the cake from the pan by running a knife along the inside edge of the pan and inverting it onto a work surface.
Carefully peel off the parchment paper.