Preheat your oven to 350°F (175°C) and prepare two 9-inch round cake pans.

In a large mixing bowl, combine all-purpose flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt. Whisk until well blended.

In a separate bowl, whisk together buttermilk, vegetable oil, eggs, and vanilla extract until smooth.

Pour the wet mixture into the dry ingredients and gently fold them together until just combined.

Gradually stir in the hot water until the batter is smooth.

Divide the batter evenly between the prepared pans and bake for 30-35 minutes, or until a toothpick comes out clean.

Let the cakes cool in pans for 10-15 minutes, then turn them out onto wire racks to cool completely.

For the blackberry compote, combine blackberries, lemon juice, and powdered sugar in a saucepan and cook over medium heat for 5-7 minutes.

Assemble the cake by stacking layers with blackberry compote between each.

Optional: Garnish with whipped cream before serving.