Spray and flour a loaf pan. Preheat oven to 350 degrees F.
In a mixing bowl, combine the flour, baking powder and salt. In another bowl, beat the butter until light and fluffy. Gradually add the applesauce, sugar and vanilla to the butter. Add the eggs 1 at a time, scraping down the sides of the bowl after each addition. Stir the flour into the butter, on low, alternately with the milk, beginning and ending with the flour.
Put 2/3 of the batter in the prepared loaf pan. Add the fudge sauce and the baking soda to the remaining batter and mix until just blended. Spoon the chocolate mixture on top of the batter in the pan and swirl with a butter knife.
Bake for approximately 1 hour or until the cake pulls away from the sides of the pan. Cool 10 minutes in the pan. Remove from the pan and cool completely.
Place the sweetener in a medium pot over low heat and reduce by 1/3 until thick.
Mix in the cocoa powder until combined and set aside to cool, (it will foam up). Place in a sealable container and refrigerate until needed up to 2 weeks.