Mix the eggs, buttermilk, oil, mayonnaise, and vanilla in a separate bowl, then add to the flour mixture and mix on medium speed for 2 minutes. Scrape the bowl as needed.
2 Eggs, ½ cup Oil, 1 cup Buttermilk, ¼ cup Mayonnaise, 1 tablespoon Vanilla extract
Bring the speed down and add the hot coffee and mix until just mixed. DO NOT OVERMIX.
1 cup Brewed coffee
The batter will be thin, and that’s okay. Pour the batter into the prepared pans, and bake for 40-45 minutes until an insert into the center comes out clean. Cool the cakes in the pan for about 15 minutes, then invert onto wire racks to cool completely before frosting.
How To Make The Ermine Frosting
This frosting is made by cooking flour, salt, and sugar in warm milk. Constantly whisk the mixture over medium heat until it comes to a simmer and thickens, which may take 5-8 minutes. Do not increase the heat, as it may burn the mixture's bottom.
Keep whisking the mixture until it has a pudding consistency. The mixture may form lumps, which is okay. Run the mixture through a strainer to remove the lumps. Pour the mixture into a bowl, cover its top with cling wrap, and let the plastic touch it. This will prevent it from forming a skin on the top of the mixture. Leave the bowl on the counter or in the fridge to let the mixture come to room temperature.
It is very important not to let the mixture become cold; if it becomes colder than room temperature, leave it out of the fridge to bring it to room temperature.
Add the soft butter in tablespoons using the paddle attachment and keep beating until all the butter is added and the mixture is smooth and creamy. Add the vanilla extract and mix. See notes for troubleshooting.
2 cups Butter, 2 teaspoon Vanilla extract
How To Make The Ganache
Bring the heavy cream to a simmer either in the microwave or over the stove. Remove it from the heat, add the semi-sweet chocolate chips, and let it sit for 5 minutes.
1 cup Heavy cream, 8 ounce Semi-sweet chocolate chips
Stir the mixture until it is smooth and all the chocolate is melted. Add the vanilla extract and mix.
1 teaspoon Vanilla extract
At this point, the mixture is too runny because the cream is still warm. Let it sit at room temperature to thicken a bit and reach the consistency of honey.
Assembly
Place one cake layer on the turn table, and drop about two cups of Ermine Frosting on the cake layer, and gently spread it over the cake. Do not bring the frosting to the side of the cake—we're not trying to frost it. Place the second cake layer over the frosting and gently press. Spread the chocolate ganache over the top of the cake and enjoy.
Notes
If the frosting is too runny and soft, it is most likely because the milk mixture was too warm when you added the butter. Place the mixture in the fridge for 15 minutes and beat again.
If it is too grainy, the mixture was too cold when you added the butter, making it harden and turn into small grains. Keep beating the mixture until the butter has warmed up, making it smoother and creamier.