Start by making the chocolate ganache. Place the chocolate chips in a heat-safe bowl.
Add the heavy cream and sugar to a small saucepan and heat over medium heat until hot and just beginning to simmer. Do not let it come to a full boil.
Pour the hot cream mixture over the chocolate chips and let it sit undisturbed for 2-3 minutes. Stir until completely smooth and glossy.
Allow the ganache to cool for about 1 hour and 30 minutes, or until thickened and spreadable. You can place it in the refrigerator to speed up the cooling process. If refrigerated, check and stir it occasionally so it doesn't become too firm.
While the ganache cools, preheat your oven to 350°F. Grease a 9-inch round cake pan and line the bottom with parchment paper.
In a large bowl, whisk together the flour, cocoa powder, salt, and baking powder until well combined.
Add the milk, vegetable oil, egg, sugar, and vanilla extract. Mix until the batter is smooth and well combined.
Slowly pour in the boiling water while mixing until fully incorporated. The batter will be thin, this is completely normal.
Pour the batter into the prepared cake pan and bake for 36 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Allow the cake to cool in the pan for about 15 minutes, then carefully remove it from the pan and transfer it to a wire rack to cool completely.
Once the cake is completely cool and the ganache has thickened, spread the chocolate ganache evenly over the top of the cake. Slice and serve.