Prepare the Chocolate Cake:
Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large mixing bowl, sift together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the buttermilk, vegetable oil, eggs, and vanilla extract. Beat on medium speed until well combined.
Reduce the speed to low and carefully add the boiling water to the batter. Mix until the batter is smooth (it will be thin).
Divide the batter evenly between the prepared pans.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.
Prepare the Creamy Filling:

In a medium bowl, beat the cream cheese until smooth.
Gradually add the powdered sugar and continue to beat until well combined.
Add the heavy cream and vanilla extract, and beat until the mixture is light and fluffy.
Chill in the refrigerator until ready to use.
Prepare the Chocolate Ganache:

Place the chopped chocolate in a heatproof bowl.
In a small saucepan, heat the heavy cream until it just begins to simmer.
Pour the hot cream over the chocolate and let it sit for 2-3 minutes.
Stir until the chocolate is completely melted and the mixture is smooth.
Stir in the butter if using. Let the ganache cool slightly before using.
Prepare the Frosting (Optional):

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