Preheat oven to 350F
Line the bottom of a 9-inch, removable bottom pan with parchment paper, and brush the sides with a little butter - set aside
Add the turbinado sugar and the 1/2 tbsp of almond flour to a small bowl, and whisk to combine - set aside
Add the all purpose flour, the almond flour, the baking powder and the salt to a large bowl, and whisk to combine - set aside
Beat the eggs and the sugar in a large bowl, using a hand mixer, until the eggs look frothy and stringy (a few minutes on medium speed)
Add the melted butter and the vanilla extract to the egg mixture, and beat a few more minutes
Add the dry ingredients to the egg mixture, and beat until combined
Add the apple chunks, and fold with a spatula to combine
Pour batter into lined pan
Decorate with the apple slices
Sprinkle with the turbinado sugar mixture, as desired
Bake for approximately 45 minutes to about an hour, or until toothpick inserted in the center comes out clean
Cool in the pan in a cooling rack for approximately 10 minutes