Preheat the oven to 350°F. Grease and flour two 9x5 inch loaf pans.
Whisk together the flour, baking powder, salt and cinnamon. Set aside.
In a large mixing bowl using an electric mixer, beat the butter, sugar and vanilla until creamy.
Add the eggs one at a time, beating well after each egg and scraping the bowl often.
Using a heavy dutyscraper or a mixing spoon, add flour mixture to egg mixture, alternating with the apple cider. Stir in the chopped apples.
Divide the batter between the prepared loaf pans and spread it evenly in the pan. Sprinkle with walnuts (if using).
Mix together the sugar and cinnamon and sprinkle over the batter.
Bake for 50-60 minutes for or until a toothpick inserted in the center comes out clean.
Notes
I weighed out 18 oz of flour, so each cup was 4.5 oz in weight. If you don't have a scale, make sure to stir and aerate the flour before measuring. Also, using 2 cups whole wheat and 2 cups all-purpose works well.