Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large bowl, combine 2 cups of all-purpose flour, 1 ½ cups of sugar, 1 cup of cocoa powder, 1 tsp of baking powder, 1 tsp of baking soda, and ½ tsp of salt.
Add 1 cup of buttermilk, ½ cup of vegetable oil, 2 large eggs, and 1 tsp of vanilla extract to the dry ingredients. Mix until well combined.
Stir in 1 cup of blackberry puree until evenly distributed in the batter.
Gradually add 1 cup of boiling water to the batter, continuing to mix until the batter is smooth and well combined.
Pour the batter evenly into the prepared cake pans.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then carefully transfer them to wire racks to cool completely.
Once cooled, frost with your favorite berry frosting or cream cheese frosting before serving.
