For the Cake:

1. Preheat your oven to 350°F and grease and flour two 9-inch round cake pans.
2. In a large bowl, whisk together the sugar, flour, cocoa powder, baking soda, baking powder, and salt until evenly combined.
3. Add the vanilla, eggs, buttermilk, and oil to the dry ingredients and stir until well combined.
4. Pour in the hot coffee and stir quickly to distribute it evenly. Don’t worry if the batter seems very thin – this is normal!
5. Divide the batter between your prepared cake pans and bake for 30-40 minutes, until a toothpick inserted in the center comes out clean.
6. Allow the cakes to cool completely before frosting.

For the Coffee Buttercream:

1. Add about 2 inches of water to a saucepan that can support your stand mixer bowl without the bowl touching the water.
2. Once the water is simmering, add the sugar, egg whites, and salt to the bowl and whisk to combine.
3. Continue heating while whisking until the sugar completely dissolves (around 120°F).
4. Transfer the bowl to your stand mixer and whisk on high speed until the mixture becomes thick and glossy with stiff peaks.
5. Reduce to medium speed and add the room temperature butter, one tablespoon at a time.
6. Turn the speed to low and add the cooled coffee, followed by the coffee grounds.
7. Increase to medium speed and mix until well incorporated and smooth.

Assembly:

1. Once cooled, slice each of the two cake layers horizontally through the middle to create four even layers.
2. Spread the coffee buttercream evenly between each layer, then cover the top and sides of the cake.
3. Smooth the frosting or create decorative swirls as desired.
4. For an extra touch, you can dust the top with cocoa powder or add chocolate shavings.