Grease a 9x13 cake pan. Preheat the oven to 350 degrees.
In a medium to large mixing bowl combine the brown sugar with the egg and softened butter. (You can mix by hand or with an electric mixer on low but do not over mix the egg.) Next, stir in the applesauce.
In a small to medium sized bowl mix the flour, salt, soda, and pumpkin spice.
Now, stir the flour mixture into the applesauce mixture until well blended.
Spread the batter into the prepared pan and bake for 15 to 20 minutes. Make sure the bars are golden brown and that a knife or toothpick comes out mostly clean to clean when inserted into the center of the bars.
Cool in the pan, preferably on a wire rack.
FROSTING: in a medium sized bowl combine the powdered sugar and butter until smooth (preferably with an electric mixer). Add in the milk and vanilla until well combined.
Spread the icing over the cooled bars evenly. Cut, serve, and enjoy!