For the cupcakes: Preheat the oven to 350 degrees. Thoroughly spray 18 muffin cups with baking spray.
To make the cake batter, combine the flour, granulated sugar and salt. Set aside.
In a separate container, combine the buttermilk, baking soda, vanilla and eggs. Stir to combine and set aside.
In a saucepan, melt the butter over medium heat. Add the cocoa powder and stir to combine. Add the boiling water, allow to bubble for a few seconds and then turn off the heat.
Pour the chocolate mixture over the flour mixture. Stir a few times to cool the chocolate. Pour the buttermilk mixture over the top and stir to combine.
Fill muffin cups just over half full (do not overfill!). Bake for 13 to 15 minutes. Allow to cool for 5 minutes in the pan, and then remove the cupcakes and allow to cool completely on a baking rack.
For the ganache: To make the ganache, heat the cream and corn syrup over medium heat. Chop the chocolate and add to a bowl. Add the vanilla to the cream mixture, and then pour the cream mixture over the top of the chopped chocolate. Whisk together until melted, smooth and glossy. Allow to cool slightly.
For the creme filling: Whip together the butter and shortening until light and fluffy.
Sift together the powdered sugar and salt and add it to the butter mixture in batches. Add the milk, then the vanilla, beating the whole time. Scrape the sides of the bowl, and beat until very light and fluffy. Put the filling into a pastry bag fitted with a medium tip.
When the cupcakes are totally cool, insert the tip of the pastry bag into the bottom of the cupcake and fill with creme filling. When cupcakes are filled, spoon ganache so that it completely coats each cupcake OR dip to coat.
Let them set before serving.