FOR THE BANANA TOPPING:
Preheat oven to 350 F (180 C) and grease a standard bread loaf pan. Set aside! In a large bowl, sift the flour and mix with baking soda, salt, cinnamon, and nutmeg. Set aside.
In a bowl of an electric mixer, cream together butter and both sugars. Add eggs, one at a time, beating after each addition until just incorporated into the batter (please, do not overbeat!!).
Beat in half of the flour mixture at low speed just until incorporated into the batter. Beat in half of the applesauce.
Beat in the remaining flour mixture, and then the other half of the applesauce until just incorporated. Mix in both the mashed bananas and vanilla. Set batter aside.
To prepare the banana topping: Place 4 tbsp butter and 3/4 cup brown sugar in a small saucepan and stir over medium heat until butter melts and the sugar has dissolved.
Without stirring, continue cooking for a few more minutes or until bubbles just start to form around the outside edges of the mixture (i.e. the sugar begins to caramelize). Stir and then pour into a loaf pan. Evenly arrange the bananas slices, flat side down, on top of the caramel.
Pour batter over bananas and bake loaf for 55-70 minutes or until a toothpick inserted in the center comes out clean.