Preheat to 325 degrees.
Grease a tube pan. For the cake, combine all the cake ingredients in a large bowl in the order given and mix well. Bake for 1 ½ hours. Shortly before it’s done, make the sauce. Melt the butter in a large saucepan, stir in the sugar, buttermilk, and baking soda, and bring to a good rolling boil, stirring constantly, Boil for 1 minute. Pour the sauce over the hot cake in the pan as soon as you remove it from the oven. Let stand 1 hour, then turn out. Takes a long time to cool but is incredibly moist and delicious! Sprinkle with powdered sugar once cooled.