Preheat oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan.
Sift flour, cocoa powder, baking soda, baking powder, and salt together in a bowl.
In another bowl, whisk eggs, buttermilk, oil, and vanilla until combined.
Carefully add boiling water to the dry ingredients mixture, whisking until incorporated.
Gradually fold the wet ingredients into the dry mixture and pour into the prepared pan.
Bake for 30-35 minutes, until a toothpick inserted in the center comes out clean.
Let the cake cool completely.
In a mixer, beat cream cheese and butter until light and fluffy.
Spread the frosting evenly over the cooled cake.
Microwave or melt the chopped chocolate until smooth to form a ganache glaze.
Drizzle the ganache over the frosted cake and let set before serving.