01 - Preheat oven to 350°F. Grease and line two 8-inch round cake pans with parchment paper.
02 - Sift together all-purpose flour, cocoa powder, sugar, baking powder, baking soda, and salt in a large bowl.
03 - Whisk eggs, whole milk, vegetable oil, and vanilla extract until smoothly combined.
04 - Pour wet ingredients into dry ingredients and mix until just combined without overmixing.
05 - Gradually add boiling water to the batter, stirring until smooth and thin in consistency.
06 - Evenly distribute batter between the prepared pans.
07 - Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean.
08 - Let cakes cool in pans for 10 minutes, then transfer to wire racks to cool completely.
09 - Place chopped dark chocolate in a heatproof bowl.
10 - Simmer heavy cream in a small saucepan then pour over the chocolate. Let rest for 2 minutes.
11 - Add unsalted butter and stir gently until chocolate melts and ganache is smooth.
12 - Allow ganache to cool and thicken slightly for 15 to 20 minutes until spreadable.
13 - Spread ganache over first cake layer, top with second layer, then cover top and sides with remaining ganache.