Chocolate Chocolate Teacake From 'Huckleberry'

Ingredients (14)

• 3/4 cup/100 g pastry flour
• 6 tablespoons/45 g all-purpose flour
• 6 tablespoons/30 g unsweetened cocoa powder
• 1 teaspoon baking powder
• 3/4 teaspoon baking soda
• 1/2 cup/120 ml strong brewed coffee, cooled
• 1/2 cup/120 ml buttermilk
• 1 teaspoon vanilla extract
• 1 3/4 cups/300 g coarsely chopped dark chocolate, 60 to 70% cacao
• 1/2 cup + 2 tablespoons/140 g unsalted butter, cubed, at room temperature
• 1 cup + 2 tablespoons/225 g sugar
• 1/2 teaspoon kosher salt
• 3 eggs
• Powdered sugar for topping (optional)