Pre-heat your oven to 350 degrees.
Peel and dice apples and set aside.
In a mixing bowl mix together flour, salt, baking soda and baking powder and set aside.
In a mixer with a paddle attachment, beat the butter and sugar together until light and fluffy. Add each egg one at a time until will blended. Slowly pour in the buttemilk and vanilla and mix until incorporated.
With a cup at a time add in the flour mixture and mix until combined.
Fold in the diced apples and chopped walnuts and pour into a greased 9x5 in. loaf pan.
To make the topping use a food processor and pulse until mixture becomes crumbly. Sprinkle on top of the bread batter.
Bake in the oven for 50-60 minutes or until a toothpick inserted into the middle comes out clean. Let it rest in the pan for about 10 minutes and then take it out to finish cooling on a cooling rack. Slice and enjoy!