I made this cake in a set of metal dry measure cups. You can use a traditional 9-inch baking pan, if you prefer. Preheat the oven to 350 degrees F.
To make the cake: Melt the butter into the coffee. When the butter has melted, whisk in the buttermilk.
Placed the eggs and sugar in the bowl of a stand mixer and place on low speed. Add the flour, salt, cocoa powder, baking powder, and baking soda 1 at a time and mix just until combined. Add the vanilla and the coffee buttermilk mixture. Mix just until combined.
If you are using dry measure cups, place the batter in a container with a spout to make it easier to pour the batter into the dry measure cups. Place the measuring cup molds onto a cookie sheet. Spray each cup with vegetable cooking spray. Fill each cup half full. Bake for 15 to 20 minutes.
To make the ganache drizzle: Heat the heavy cream in a 2-quart heavy-bottomed saucepan until bubbles begin to form around the edge of the pan. Place the chopped chocolate in a medium-size mixing bowl. Make a ganache by pouring about half of the hot cream over the chocolate and letting it sit for 30 seconds to melt the chocolate. Then, slowly whisk until smooth and homogenous. Do not add all of the hot cream to the cold chocolate at once. The shock of the temperature extremes will cause the fat in the chocolate to separate. If the ganache separates, it loses its elasticity, collapses, and becomes very liquid. I use a hand-held immersion blender to ensure a smooth ganache and to keep the emulsion of the chocolate. Add the remaining cream gradually and mix until all of the hot cream is incorporated and the ganache is smooth and homogenous.
Unmold the cakes and let cool on a wire rack placed over a parchment paper lined baking sheet. When cool, stack the cakes on top of each other with the largest cake on the bottom layer. Placing the cakes on a wire rack placed over a parchment paper lined baking sheet. Use an offset spatula to spread the ganache over the cakes letting the excess drizzle over the sides. Use an offset spatula to move the cakes to the presentation plate.
Make the chocolate curls: Use a block of white chocolate. Pull a vegetable peeler over the edge to create chocolate curls. Use the curls to decorate the cakes.