Chop the chocolate and transfer it to a heatproof bowl. In a small saucepan add the heavy cream. Set the pan over medium heat. Heat the cream until simmering and pour it over the chocolate. Let it sit for one minute and then whisk until smooth. Add the butter, vanilla and rum and whisk until combined. Cover the top of the ganache with plastic wrap and set aside.
Red Velvet Cupcakes
Preheat the oven to 350°F. Line standard muffin tins with paper liners.
In a medium bowl add the cake flour, cocoa, cinnamon and salt. Whisk to combine and set aside.
In a stand mixer fitted with the paddle attachment, add the sugar and butter. Turn the mixer to medium-high speed and mix until light and fluffy, 2-3 minutes. Scrape down the bowl using a spatula.
Add the egg on low speed and mix until just combined. Mix in the red food coloring and vanilla. Add the flour mixture in three batches, alternating with adding the buttermilk. Mix until combined, scraping down the bowl as needed.
In a small bowl combine the baking soda and vinegar. Add the mixture to the batter and mix on low speed until just combined.
Divide the batter evenly among the lined cups, filling each 3/4 full.
Place the cupcakes in the oven and bake, rotating the pan halfway through, for 15-18 minutes, or until a cake tester inserted in the center comes out clean. Transfer the pan to a baking rack to cool completely before removing the cupcakes.
Ginger Buttercream
While the cakes are cooling, make the buttercream. In a stand mixer fitted with the paddle attachment, add the butter and cream cheese. Turn the mixer to high and mix until light and fluffy, 2-3 minutes. Add the powdered sugar and beat on high speed for 2-3 minutes more. Add the vanilla paste, grated ginger and salt. Mix until thoroughly combined.
Assembly
Using a serrated knife, cut out a narrow, cylindrical well at the center of each cupcake. (You want to go most of the way down the cupcake but don’t cut through the bottom.)
Once the ganache is a pliable consistency, you can either place the ganache filling into a piping bag and fill each cupcake, or simply use two spoons: scoop with one spoon, and push the ganache into the hole with the other spoon.
Pipe or spread the buttercream over the tops of the cupcakes, then sprinkle the chopped crystallized ginger over the tops of the cupcakes and serve.