Beat yolks and icing sugar for 1/2 h, then add in ground almond, mix well, set aside

Beat egg whites with icing sugar until firm soft peak, then add in graham cracker crumbs, fold slowly

Combine egg white mixture into yolk mixture, and pour batter on a square baking pan that is lined with greased aluminum foil

Sprinkle halved grapes all over batter and bake at 350 F for at least 1/2 h or until golden brown (knife inserted comes out clean)