Preheat your oven to 350°F (175°C). Grease the cake pans and line the bottom with parchment paper.
In a large bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Mix well.
Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat on medium speed for about 2 minutes until well combined.
Carefully stir in the boiling water. The batter will be thin, but this is normal. Pour the batter evenly into the prepared cake pans.
Bake in the preheated oven for 25-30 minutes or until a toothpick inserted in the center comes out clean. Allow cakes to cool in the pans for 10 minutes before transferring to a cooling rack.
While the cakes are cooling, prepare the ganache. In a saucepan, heat the heavy cream over medium heat until it begins to simmer. Remove from heat.
Add the chopped chocolate to the hot cream and let it sit for a few minutes. Stir until the chocolate is fully melted and smooth. If desired, add butter for added richness and gloss.
Once the cakes are completely cooled, level the tops if necessary. Place one cake layer on a serving plate and pour a portion of the ganache over it, spreading it evenly.
Top with the second cake layer and pour the remaining ganache over the top and sides of the cake, smoothing it out with a spatula.
Allow the ganache to set slightly before slicing and serving.