Place the apple slices in a bowl and sprinkle with the Vin Santo and the granulated sugar. Cover and set aside for 1 hour. Mix together both types of flour, the egg yolk, and the white wine. Beat the egg white in a separate bowl until fluffy. Fold the egg white gently into the flour mixture. Drain the apples and mix gently into the batter. Heat 1/2-inch of vegetable oil in a heavy skillet over medium heat. Drop a 5-inch round of batter in the skillet, cook until golden brown on one side, flip and cook likewise on the other side. This should take about 3 minutes (1 1/2 minutes per side). Remove, drain, dust with the confectioners' sugar, and serve.