Preheat the oven to 350°F (175°C). Grease and flour the two 9-inch round cake pans. Line the bottom with parchment paper for easy removal.
In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Mix well until evenly combined.
Add the eggs, whole milk, vegetable oil, and vanilla extract to the dry ingredients. Beat with an electric mixer on medium speed for about 2 minutes until well blended.
Gradually stir in the boiling water. The batter will be thin but that is normal.
Divide the batter evenly between the prepared cake pans. Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean.
Once baked, remove the cakes from the oven and let them cool in the pans for 10 minutes. Then, remove from pans and transfer to a cooling rack to cool completely.
For the ganache, heat the heavy cream in a saucepan over medium heat until it just begins to simmer. Remove from heat and add the chopped dark chocolate and butter. Stir until smooth and glossy.
Once the cakes are completely cool, place one layer on a serving plate. Spread a layer of ganache on top. Place the second layer on top and pour the remaining ganache over the top, allowing it to drip down the sides.
Let the ganache set for a bit before slicing the cake. Enjoy!