Place 1+1/3 of the pecans in a blender or food processor and grind them to a nut flour consistency.
Whisk the ground pecans together with the flours and baking powder and set aside.
Beat the butter and brown sugar together until creamy. About 3 minutes.
Add the eggs one at a time, making sure each is fully combined into the batter before adding the next. Scrape down the sides of the bowl to make sure everything is well combined.
Fold in the chopped apples. The batter will be thick so fold them in as gently as you can.
Transfer the batter to the prepared baking pan. Arrange the remaining pecan halves over the top.
Remove from the oven, let cool in the pan. Remove from pan transfer to a serving plate, cut and serve.