Preheat the oven: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or line the bottoms with parchment paper.

1. Mix the dry ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cocoa powder. Set aside.
2. Cream the butter and sugar: In a large bowl, beat the softened butter and sugar together using an electric mixer on medium speed until light and fluffy, about 3-4 minutes.
3. Add eggs and vanilla: Beat in the eggs, one at a time, followed by the vanilla extract, ensuring each is well combined before adding the next.
4. Alternate adding dry ingredients and buttermilk: Gradually add the dry ingredients to the wet mixture in 3 parts, alternating with the buttermilk in 2 parts. Begin and end with the dry ingredients. Mix until just combined.
5. Add boiling water: Stir in the boiling water until the batter becomes smooth and thin. This step helps the cake stay moist and tender.
6. Bake the cake: Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a toothpick inserted into the center of the cakes comes out clean.
7. Cool the cakes: Let the cakes cool in the pans for 10 minutes, then remove from the pans and transfer to a wire rack to cool completely.
8. Make the ganache: In a small saucepan over medium heat, bring the heavy cream to a simmer. Place the chopped chocolate in a heatproof bowl, pour the hot cream over the chocolate, and let it sit for 2-3 minutes to melt the chocolate. Stir until smooth and glossy. Stir in the butter until fully incorporated.
9. Cool the ganache: Let the ganache sit at room temperature for about 10-15 minutes, or until it thickens slightly but is still pourable.
10. Assemble the cake: Place one layer of the cooled cake on a serving plate. Pour a generous amount of ganache over the top, spreading it evenly to cover the top and allow it to drip down the sides. Place the second layer on top and pour the remaining ganache over the top.
11. Chill the cake: Let the cake sit at room temperature for about 30 minutes to allow the ganache to set. If you want a firmer ganache, place the cake in the refrigerator for 10-15 minutes.
12. Serve: Slice and serve the cake once the ganache has set. Optionally, top with fresh berries, whipped cream, or chocolate shavings for added elegance.