Preheat oven 350 F.
Grease and flour a loaf pan. Set aside.
Mix together brown sugar and cinnamon. Set aside.
Sprinkle apples with 3 teaspoons of cinnamon sugar mixture. Set aside.
In a large bowl cream together butter and granulated sugar.
Add eggs and vanilla extract.
Fold in applesauce.
In a separate bowl stir together flour and baking powder.
Add flour mixture to the wet mixture JUST until combined.
Stir in buttermilk. (Batter will and should be slightly lumpy. Do not over stir)
Place half of the batter evenly into the loaf pan.
Spread on half of the apple mixture.
Sprinkle some cinnamon-sugar mixture over apples evenly just enough to cover. (FYI: You will have plenty of cinnamon-sugar mixture left over. Save it for another loaf)
Press apples into batter very slightly.
Lay a few pieces of thinly sliced butter on top.
Repeat layers. Remember to press the apples gently into the batter very slightly. (Sometimes I like to gently glide a knife down through the batter to blend the layers a bit.)
Bake on middle rack for 50-60 minutes.
Let loaf rest in pan for about 15 minutes before removing from pan to let cool off completely on a cooling rack.
While loaf is cooling combine powdered sugar with heavy cream until it is a glaze consistency.
Drizzle glaze over completely cooled bread and let the glaze sit to firm up.
Slice and serve!