Preheat oven to 350.
Sift together flour, salt, baking powder, baking soda, and cinnamon. Set aside.
Chop walnuts into small pieces and set aside.
Peel, core and slice the apples into quarters. Slice each quarter into ¼-inch thick squares. Set aside.
Cream butter and sugar on ½ of full mixing speed.
Add in eggs and beat on ¾ speed until mixture fluffs up.
Use a rubber spatula to catch the unmixed sides and bottom and push in to beaters.
Turn mixer speed down to 2 or 3 and immediately add in half of flour mixture, then the milk and then the remaining flour mixture.
Use the rubber spatula in the same way.
Wasting no time, add in apples and then walnuts.
Pour right into one non-stick 9 by 5 by 3 inch loaf pan and bake for 1 hour to 1 hour and 20 minutes.
Test with a toothpick down the center for doneness.