Preheat your oven to 325 degrees F. Spray two 8-inch cake pans with cooking spray and line them with parchment paper. Spray again. Set aside.
In a stand mixer fitted with the paddle attachment, combine flour, sugar, cocoa powder, baking soda, baking powder, and salt. Mix on low until evenly combined.
In a small bowl, whisk together eggs, buttermilk, hot water, vanilla extract, and vegetable oil until evenly combined.
With the mixer on the lowest speed, pour the liquid ingredients into the dry ingredients and mix just until combined. Scrape the bottom of the bowl with a rubber spatula to ensure even mixing.
Divide the batter evenly between the prepared pans and bake for 30-33 minutes. To check to see if the cake are done, insert a toothpick and it is done when the toothpick comes out or a few crumbs. You want to aim for a few crumbs. Allow the cakes to cool in the pans for 15 minutes, then transfer them to a cooling rack to cool completely.
Once the cakes are at room temperature, level the tops if needed, wrap them in plastic wrap, and freeze in preparation for frosting.
For the frosting:
In a medium saucepan, melt the chocolate and butter together until completely smooth. Add cocoa powder and whisk. Let cool for 15-20 minutes.
Using a whisk, add in the powdered sugar. The frosting will seem thin but will thicken as it comes to room temperature. Let it sit for up to 30 minutes until spreadable.
Once the frosting is thick and spreadable, you are ready to frost your cake.
Assembly:
Ensure that your cake layers have cooled completely before assembling. Level the cakes if needed.
Start by placing a cake layer bottom side down on your serving platter, cake board, or cake stand.
Spread a generous layer of chocolate frosting evenly over the top of the first cake layer. It's okay if it goes over the edge of the cake. Use an offset spatula to make it smooth and level.
Repeat this step, placing the second cake layer bottom side up this time.
Apply a thin layer of frosting around the entire cake and freeze for 10 to 15 minutes.
Once the crumb coat is set, finish frosting and decorating the cake with the remaining frosting.