Preheat your oven to 350 degrees F (175 degrees C). Prepare three 8-inch round cake pans by greasing them thoroughly, lining the bottoms with parchment paper, and greasing the parchment as well. Dust each pan with flour, shaking out the excess.
In the bowl of an electric mixer, combine 2½ cups of all-purpose flour, 3 cups of granulated sugar, 1 cup of Dutch-process cocoa powder, 1 tablespoon of baking soda, 1½ teaspoons of baking powder, and 1½ teaspoons of salt. Sift these ingredients together to ensure there are no lumps—this will give your cake a beautiful, even texture.
In a separate medium bowl, whisk together 3 eggs, 1½ cups of buttermilk, 1½ cups of hot strong black coffee, ¾ cup of vegetable oil, and 4½ teaspoons of vanilla extract. The mixture should be smooth and uniform.
Pour the wet ingredients into the dry ingredients and mix on medium speed for about 2 minutes. The batter will be quite thin, but that’s perfectly normal. Scrape down the sides of the bowl and mix for an additional 20 seconds to ensure everything is well combined.
Divide the batter evenly among the prepared cake pans. Use a spatula to smooth the tops if needed. Place the pans in the oven and bake for 20 minutes.
After 20 minutes, rotate the pans in the oven for even baking. Continue to bake for an additional 12 minutes or until a toothpick inserted into the center of one of the cakes comes out almost clean with a few moist crumbs.
Once baked, remove the pans from the oven and let the cakes cool in the pans on a wire rack for about 20 minutes. After cooling, carefully turn the cakes out onto the cooling racks to cool completely.
For the frosting, place 8 ounces of finely chopped semisweet chocolate in a microwave-safe bowl. Microwave in 30-second increments on 50% power, stirring after each interval, until melted and smooth. Let it cool to room temperature.
In the bowl of a stand mixer, using the whisk attachment, beat 2 cups of unsalted butter on medium-high speed for about 5 minutes until light and fluffy, stopping to scrape down the sides of the bowl as necessary.
Reduce the mixer speed to medium-low and slowly add 5 cups of powdered sugar. Once incorporated, add the melted chocolate and 2 teaspoons of vanilla extract. Beat on medium-high speed for an additional 2 minutes until fluffy and smooth.
To assemble, place one layer of cake on a serving platter. Spread 1 cup of frosting evenly over the top. Add the second cake layer and repeat the process. Top with the final cake layer upside down and frost the top and the sides of the cake as desired. Enjoy your beautifully crafted Chocolate Cake!