Preheat your oven to 375°F (190°C). Grease and flour two 8" cake pans then set aside.

In a large mixing bowl whisk together the flour, sugar, cocoa, baking soda, baking powder, and salt until fully combined.

In a different mixing bowl, mix together the milk, oil, eggs, vanilla, and sourdough discard. Whisk until the sourdough discard is fully dissolved and everything is fully incorporated.

While stirring continuously, slowly add the wet ingredients to the dry until the batter is as lump free as possible. Pour the hot coffee in and stir, scraping down the sides as needed, until your ingredients are fully combined. The batter will be very thin, this is just how we want it!

Pour the batter evenly into the cake pans and bake for 35 to 40 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 30 minutes before turning them out onto a cooling rack to finish cooling.

Using a stand mixer with the paddle attachment or a hand mixer, beat the room temperature butter until it is smooth and creamy.

Mix in the powdered sugar a little at a time until about half of it is incorporated into the butter. Then add in the vanilla and milk. This will thin out the frosting and allow you to more easily incorporate the rest of the powdered sugar.

Alternate adding the remaining powdered sugar and cocoa powder a little at a time, scraping down the sides of the bowl as needed. Beat until the frosting is light and fluffy.

Once the layers are completely cooled, you can assemble and frost the cake. Set one layer on cake plate flat side facing up. Spread about ¼ of the frosting evenly across the cake layer.

Place the second layer on top of the first with the flat side facing down. Spread the rest of the frosting evenly over the top and sides of the cake.