Preheat the oven to 350°F (175°C). Line a cupcake pan with paper liners.

In a large mixing bowl, whisk together all-purpose flour, cocoa powder, sugar, baking powder, baking soda, and salt.

Cream the softened butter until light and fluffy, then add eggs one at a time, mixing well after each.

Stir in vanilla extract and buttermilk until the batter is smooth.

Gradually add dry ingredients to wet ingredients, stirring gently until just combined.

Fold in the blackberries and dark chocolate chips.

Scoop the batter into cupcake liners, filling each about two-thirds full.

Bake for 20-25 minutes until a toothpick comes out clean.

Allow to cool in the pan for about 10 minutes, then transfer to wire racks to cool completely.

Prepare a frosting of your choice while the cupcakes cool if desired.