For the Chocolate Cake:

1. Preheat the oven to 350°F (175°C). Grease and line two 9-inch round cake pans with parchment paper.
2. In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
3. In another bowl, beat together sugar, eggs, buttermilk, oil, and vanilla extract until well combined.
4. Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.
5. Stir in the hot coffee or boiling water, mixing until the batter is smooth. The batter will be thin, which is normal.
6. Divide the batter evenly between the prepared cake pans.
7. Bake for 30–35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
8. Let the cakes cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely before frosting.

For the Vanilla Icing:

1. In a large bowl, beat the butter with an electric mixer on medium speed until smooth and creamy (about 2–3 minutes).
2. Gradually add the powdered sugar, one cup at a time, mixing on low speed.
3. Stir in the vanilla extract and a pinch of salt to enhance the flavor.
4. Add the heavy cream (or milk), one tablespoon at a time, until the frosting reaches a smooth and spreadable consistency.
5. Increase the speed to high and whip for 2 minutes until light and fluffy.

Assembling the Cake:

1. Place one cake layer on a serving plate and spread a thick layer of vanilla icing evenly on top.
2. Place the second cake layer on top and frost the entire cake, using an offset spatula for a smooth finish.
3. Decorate as desired with chocolate shavings, fresh berries, or a dusting of cocoa powder.
4. Slice and serve!