Sift flour, soda, baking powder, and salt together.
Cream shortening with sugar until fluffy. Add eggs one at a time, beating to incorporate fully between each addition.
Blend in chocolate and vanilla.
Add sifted dry ingredients and milk alternately, starting with 1/3 of the flour mixture, then ½ of the milk, 1/3 more flour mixture, and then the remaining milk, ending with the final 1/3 flour mixture. Beat for approximately 20 seconds between each addition, making sure the ingredients are well blended after each addition.
Pour the batter into the prepared cake pans. I use a scale to ensure that each pan has approximately the same amount of batter.
Bake for approximately 18 – 24 minutes or until the cake tester comes clean. This cake is delicate, and you do not want to overbake it. The 9” pan will cook faster (thinner layer of batter) – so test at 18 minutes. When the cake tester comes out clean, remove it from the oven and let rest on wire cooling racks for 3 to 5 minutes.
Turn out onto a wire rack to cool. You can wrap the cake in plastic and refrigerate it if making it a day or two ahead. It can also be frozen for future use.