Dark Chocolate Cupcakes

INGREDIENTS

• :
• 8 tablespoons (1 stick) unsalted butter, cut into 4 pieces
• 2 ounces bittersweet chocolate, chopped
• ½ cup (1.5 ounces) Dutch-processed cocoa powder
• ¾ cup (3.75 ounces) all-purpose flour
• ½ teaspoon baking soda
• ¾ teaspoon baking powder
• 2 eggs
• ¾ cup (5.25 ounces) granulated sugar
• 1 teaspoon vanilla extract
• ½ teaspoon table salt
• ½ cup (4 ounces) sour cream
• 1 cup confectioners' sugar
• 1 cup creamy peanut butter
• 5 tablespoons unsalted butter, at room temperature
• ¾ teaspoon vanilla extract
• ¼ teaspoon kosher salt
• ⅓ cup heavy cream