In a saucepan over medium heat, combine butter, sweetener, and molasses. Heat just until bubbly then pour in heavy whipping cream and remove from heat. Stir. Pour mixture into a 9 inch round cake pan. Spread chopped pecans evenly over mixture and set aside.
Preheat oven to 350 degrees.
Beat together the cake ingredients together until well blended. Allow to sit for a few minutes and then stir again. Gently spoon batter over pecans mixture in the pan.
Bake for 30 min or until an inserted knife comes out clean. Allow to rest for 5 minutes and then invert cake onto a serving plate or tray.
Whisk 1/2 cup heavy cream until thickened. Add 1 tablespoon sweetener and 1/2 tsp vanilla. Spread onto cooled cake just before serving. Garnish with additional pecans and chocolate shavings if desired.