For the cupcakes:

• 1 cup all-purpose flour
• 1/2 cup unsweetened cocoa powder (preferably dark/Dutch-processed)
• 1 tsp baking soda
• 1/2 tsp baking powder
• 1/4 tsp salt
• 1 cup granulated sugar
• 2 large eggs
• 1/2 cup vegetable oil or melted butter
• 1/2 cup buttermilk
• 1 tsp vanilla extract
• 1/2 cup strong brewed coffee or hot water
• 1 cup fresh or frozen blackberries (chopped or whole)

For the frosting:

• 1 cup unsalted butter, softened
• 3 cups powdered sugar
• 6 oz dark chocolate (60–70% cocoa), melted and cooled
• 2–3 tbsp heavy cream or milk
• 1 tsp vanilla extract
• 2–3 tbsp blackberry jam or puree (optional)