Preheat oven to 350°F. Line 10-1/2 in. x 15 1/2 in. x 1 in. with parchment paper and spray with vegetable pan spray.
In small bowl, combine flour and baking powder. In large bowl, whip egg whites and 1/4 cup of the sugar with electric mixer until stiff but moist peaks form. In large bowl, whip egg yolks, vanilla and remaining 1/4 cup sugar until creamy and lightened in color, about 4-5 minutes. Fold egg whites into the yolk mixture gently but thoroughly. Fold in flour.
Pour batter into prepared pan and carefully spread to edges in an even layer.
Bake 10 to 12 minutes, or until golden brown at edges. Cool 10 minutes in pan. Loosen sides of cake with knife; invert cake onto a cooling rack. Peel off parchment paper. Flip cake back over.
Starting at a short edge, roll up cake with kitchen towel. Transfer rolled cake to cooling rack; cool completely.
To fill cake, gently unroll cake. Cover with thin layer of buttercream icing. Gently reroll cake without parchment paper; cut off ends of roll. Transfer to cake board or serving plate.