Preheat oven to 375 degrees F. Grease a loaf pan. Sift flour with baking powder. cream butter. Slowly add Sugar to butter, beating well after each addition. Add egg yolks to butter mixture, one at a time, and beat well after each addition. Add vanilla. Add dry ingredients in 2 or 3 parts, alternating them with the milk. Whip egg whites until stiff. Gently fold them into the batter. Turn the batter into the loaf pan. Press the Apple slices deeply into the batter. Sprinkle with Sugar & cinnamon mixture. Bake about 30 – 50 minutes, or until tester comes out dry.