Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large mixing bowl, sift together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat on medium speed for 2 minutes until smooth.
Carefully stir in the boiling water. The batter will be thin; this is normal.
Divide the batter evenly between the prepared pans.
Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cakes from the oven and allow them to cool in the pans for 10 minutes.
Turn the cakes out onto a wire rack and cool completely.
To prepare the chocolate ganache, place the chopped semisweet chocolate in a medium heatproof bowl.
Heat the heavy cream in a small saucepan over medium heat until it just begins to simmer.
Pour the hot cream over the chopped chocolate and let it sit for 5 minutes.
Stir gently until the mixture is smooth and glossy. Let the ganache cool to room temperature but still pourable.
Place one cake layer on a serving plate. Spread a thin layer of ganache over the top.
Place the second cake layer on top and pour the remaining ganache over the cake, allowing it to drip down the sides.
Use an offset spatula to smooth the ganache evenly over the top and sides of the cake.
Let the ganache set at room temperature for 30 minutes before serving.