01 - Preheat oven to 350°F. Grease and line two 9-inch round cake pans with parchment paper.
02 - Sift together flour, cocoa powder, sugar, baking powder, baking soda, and salt in a large bowl.
03 - Add eggs, milk, oil, and vanilla extract to the dry mixture. Beat on medium speed for 2 minutes until combined.
04 - Stir in boiling water carefully; the batter will be thin.
05 - Pour batter evenly into prepared pans.
06 - Bake for 30 to 35 minutes until a toothpick inserted in the center comes out clean.
07 - Allow cakes to cool in pans for 10 minutes, then transfer to wire racks to cool completely.
08 - Place chopped chocolate in a heatproof bowl. Heat cream until just simmering and pour over chocolate. Let sit 2 to 3 minutes, add butter, then stir until smooth and glossy. Cool until thick but pourable.
09 - Place one cake layer on a serving plate, spread ganache on top. Add second layer, then cover top and sides with ganache.
10 - Let cake set at room temperature or refrigerate for a firmer finish before slicing.