Preheat oven to 350 degrees. Spray two 9 inch round cake pans with nonstick cooking spray. Place a square of parchment paper in the middle of the pan and spray the tops of the parchment paper.
In a microwave-safe medium bowl, add in the water and butter. Microwave for 2 and half minutes.
Add in the vegetable oil and cocoa powder and whisk until smooth.
Add in sour cream and vanilla and continue to whisk until the sour cream in incorporated.
In a separate bowl, add in cake flour, sugar, baking soda, and baking powder. Whisk until combined.
Pour the cocoa mixture in with the dry ingredients. Add in the lightly beaten eggs. I add the eggs now because I don't want them to cook in the hot cocoa mixture. Whisk until everything is combined. Try to whisk out most of the lumps.
Divide the batter into the two 9 inch cake pans. I wrapped my pans with Wilton's even bake strips.
Bake for 30 minutes or until they're done. Place a toothpick in the center of the cake and if it comes out clean or with moist crumbs it's done.
Let the cake cool in the pan for about 15 minutes and then turn onto a cooling rack to finish cooling.
In a medium microwave-safe bowl, add in chocolate chips and heavy cream. Microwave 45 seconds and mix with spatula. Repeat until the ganache is smooth and completely melted. Place in the fridge for 2-3 hours until the ganache hardens.
In a double boiler, add the egg whites and granulated sugar.
Stir until the sugar is dissolved. This is when the egg whites reach about 160 degrees.
Pour into the stand mixer bowl, and whip with a whisk attachment on high. The meringue needs to come to stiff peaks. If you turn the whisk upside down and the peak stands straight up, you've reached the stiff peak stage.
Add all at once the shortening and butter. Beat until it all comes together. It will thicken up at this point. If the mixture looks like it curdled, keep mixing. It will come back together.
Add the vanilla and 1 cup of the prepared milk chocolate ganache. Mix until combined.
The frosting should be thick and creamy. If it looks separated, keep mixing. It will come back together.
On the first layer of cake, make a dam with the chocolate buttercream. I used a piping bag and a coupler to achieve this.
Fill the cake with the rest of the milk chocolate ganache. Spread the ganache so it's even.
Add on the top layer of the cake and use the spatula to go around the dam to smooth it out.
Spread the buttercream over the cake until you have the desired effect.