Preheat oven to 350˚F. Cream together sugar and shortening for cake using electric mixer. Add eggs one at a time and mix until pale yellow and just beginning to get frothy. Add buttermilk and vanilla and stir until just combined.
Sift flour, baking soda, and salt into wet ingredients and stir until uniform in color. Pour half of cake batter into a greased 9″x13″ deep-sided baking pan. Combine filling ingredients and sprinkle filling over batter.
Pour in remaining batter and then take a butter knife and swirl the filling throughout the batter. Do not fully blend the two layers as you want swirls through the whole cake.
Bake for 30 minutes or until toothpick inserted in center comes out clean. While cake is baking heat icing ingredients in small saucepan over low. Poke holes nearly all the way to the bottom of cake using a fork, chopstick, or wooden spoon handle.
Pour icing over cake while it’s still warm. Allow to cool for 20 minutes before cutting into squares to serve.